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Corporation 


33  WIST  MAIN  STRUT 

WnSTIR.N.Y.  MSM 

(716)t72-4S03 


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CIHM/ICMH 

Microfiche 

Series. 


CIHIVI/ICIVIH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historicai  IMicroreproductions  /  Institut  Canadian  da  microreproductions  hittoriquat 


\ 


\ 


T«chnical  and  Bibliographic  Notaa/Notas  tachniquaa  at  bibliographiquaa 


Tha  Inatituta  haa  attamptad  to  obtain  tha  baat 
original  copy  availabia  for  filming.  Faaturaa  of  thia 
copy  wvhicti  may  ba  bibliographically  uniqua. 
•vhieh  may  altar  any  of  tha  imagaa  in  tha 
raproduction.  or  which  may  significantly  changa 
tha  uaual  mathod  of  filming,  ara  chackad  balow. 


□   Coiourad  covara/ 
Couvartura  da  coulaur 


pn   Covars  damagad/ 


Couvartura  andommagia 


□   Covars  rastorad  and/or  laminatad/ 
Couvartura  raatauria  at/ou  pallicuiAa 

□    Covar  titia  missing/ 
La  titra  da  couvartura  manqua 


r~n   Coiourad  maps«' 


a 


n 


D 


Cartaa  gtegraphiquaa  ti  coulaur 


Coiourad  inic  (i.a.  othar  than  blua  or  black)/ 
Encra  da  coulaur  (i.a.  autra  qua  blaua  ou  noira) 


Coiourad  plataa  and/or  iliuatrations/ 


I     I    Planehaa  at/ou  illuatrationa  an  coulaur 


Bound  with  othar  matarial/ 
RaliA  avae  d'autraa  documants 


Tight  binding  may  cauaa  shadows  or  diatortion 
along  intarior  margin/ 

La  f  liura  sarrAa  paut  cauaar  da  I'ombra  ou  da  la 
distorsion  la  kMig  da  la  marga  intiriaura 

Blank  laavas  addad  during  rastoration  may 
appaar  within  tha  taxt.  Whanavar  possibia,  thasa 
hava  baan  omittad  from  filming/ 
II  sa  paut  qua  cartainaa  pagas  blanches  ajoutAas 
lors  d'una  raatauration  apparaiasant  dana  la  taxta. 
maia.  lorsqua  cala  Atait  possibia.  caa  pagaa  n'ont 
paa  *ti  filmiaa. 


L'Inatitut  a  microfilm^  la  maiiiaur  axamplaira 
qu'il  lui  a  it*  poasibia  da  sa  procurer.  Las  details 
da  cat  axamplaira  qui  sont  paut-Atra  uniquas  du 
point  da  vua  bibliographiqua,  qui  pauvant  modifier 
una  image  reproduite.  ou  qui  pauvant  exiger  une 
modification  dans  la  m^thoda  normaia  dc  filmaga 
sont  indiqute  d-dessous. 

□   Coloured  pagaa/ 
Pagae  da  coulaur 

□   Pagaa  damaged/ 
Pagaa  andommagiaa 

□   Pages  restored  and/or  laminated/ 
Pages  reataurias  at/ou  peiliculies 

0    Pages  discoloured,  stained  or  foxed/ 
Pages  dicolories,  tacheties  ou  piqutes 

Pagaa  dttachies 

Showthroughy 
Transparence 

Quality  of  prir 

Quality  inAgale  de  I'impression 

Includes  supplementary  matarii 
Comprend  du  metiriel  supplimentaira 

Only  edition  available/ 
Seuie  Mition  disponibie 


[~n  Pages  detached/ 

r7|  Showthrough/ 

n~]  Quality  of  print  variea/ 

r~n  Includea  supplementary  materiel/ 

|~n  Only  edition  available/ 


n 


Pages  wholly  or  partially  obscured  by  errata 
slips,  tissues,  etc.,  have  been  refilmed  to 
ensure  the  best  possible  image/ 
Lea  pages  totalement  ou  partiellement 
obscurcies  par  un  feuiilet  d'errata,  une  pelure. 
etc.,  ont  iti  filmAes  k  nouveau  de  fapon  i 
obtenir  la  meilleure  imege  possible. 


D 


Additional  comments:/ 
Commentaires  suppiimantairas: 


Paginstion  as  follows  :  [163]  -  [193]  p. 


This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  document  eat  film*  au  taux  de  rMuction  indiqui  ci-deaaous. 


10X 

14X 

itx 

ax 

26X 

30X 

y 

12X 


16X 


aox 


24X 


28X 


32X 


Th«  eopy  filmed  h&n  hM  b««n  r«produe«d  ttianks 
to  tlM  gwMrosity  of: 

Ubrary  of  PwtianMnt  Mid  tiM 
National  LNMrary  of  Canada. 

Tho  imogoo  oppooilm  horo  aro  tiM  boot  quality 
poaaibla  cowldorlng  tho  oondMon  and  lofibMty 
of  tho  orl^nal  eopy  ond  in  liooping  with  tho 
filming  contraot  apooHleatlono. 


L'oxomplairo  fllmA  fut  roproduit  grioo  A  la 
gdndrooltA  do: 

La  Bibliothiqaa  du  Pariamant  at  la 
Bibliothkiua  national  du  Canada. 


aulwantaa  ont  4id  roprodultaa  avoe  to 
aoin,  eompto  tami  do  lo  oondMon  at 
'  do  I'osompMro  fUmd.  ot  it 
avoe  loo  eondltione  du  eontrat  do 


oo  10  notioto 


Original  coploo  in  printod 
bofpnning  with  tho  front  eovor  and  ending  on 
tho  ieet  pogo  with  a  printod  or  ilHietrated  impree- 
alon,  or  tho  book  eovor  when  approprloto.  All 
other  orlginol  eopiee  aro  fRmod  beginning  on  tho 
firat  pogo  with  a  printed  or  Hhietrated  impree 
alon.  and  ending  en  tho  loot  pogo  %irith  e  printed 
or  illuetretod  Impreeeion. 


parlo 
dom 

plot. 


!■  (MrnWrO 


origlnaux  dont  le  eouverture  en 
imprimoo  aont  fHmee  en  eommon^ent 
plat  ot  en  tomdnent  aolt  per  la 
page  qui  eomporto  uno  emprointo 

ou  dlNuetration.  aolt  per  le  aeoond 
io  eoe.  Toue  lee  eutree  OKompleiree 
aont  fNmde  en  eommon^ent  per  le 
pogo  qui  eomporto  uno  emprointo 

ou  dlNuetration  ot  en  termlnent  per 
pogo  qui  eomporto  uno  toUo 


Tho  loot  recorded  frame  on  aooh 
ahoN  eentain  tho  aymbol  ^»( 
TINUIO").  or  the  aymbol  ▼  d 


"COW- 
INO"). 


Un 


le 
aymbolo  ▼ 


auiventa  apporaltra  aur  la 
da  cheque  mieroflcho.  aolon  lo 
»•  aignmo  "A  SUIVRE",  lo 
aigniflo  "RN". 


MopOt  ptotoOt  ehenOt  etc.>  may  bo 
different  reduction  retloo.  Thoeo  too 
entirely  included  in  one  oupoeuro 

beginning  in  tho  uppof  loft  hond 
ngnf  ana  lop  id  eononi.  ■■  many 
required,  ino  following  dtegromo 


lorgotobo 
nod 
loft  to 


!•  ploneheOt  tableouji<  etc..  pouvent  etre 
fHmde  A  doo  taux  da  rdduetion  diffdrentt. 
Lorequo  lo  document  eet  trap  grand  pour  Atre 
roproduit  en  un  aoul  oMchd.  II  eet  fNmd  A  pertir 
do  Tangle  aupdriour  gaudio.  do  gouoho  *  draito, 
ot  do  hout  en  boe«  en  prenawit  le  nombre 
dlmogoe  nAceeaalra.  Lee  diogrammee  auiventa 
IHuotront  la  methodo. 


1 

2 

3 

32X 


1 

2 

3 

4 

5 

6 

n 


BULLETIN  OF  THE  QEOLOGICAL  SOCIETY  OF  AMERICA 

Vol.  1,  pp.  163-174;  176-194 


NOTE  ON  THE  PRE-PALEOZOIC  SURFACE  OF  THE  ARCHEAN 

TERRANE8  OF  CANADA 

THE  INTERNAL  RELATIONS  AND  TAXONOMY  OF  THE 
ARCHEAN  OF  CENTRAL  CANADA 


BT 


ANDREW  C.  LAWSON 


WASHINGTON 

PUBLISHED  BY  THE  SOCIETY 

Mabch,  1890 


'f   ?*■• 


/ 


NC 


Intrc 

The: 

( 

C 

The] 

C 

Rovie 

Geneii 


S 
Discus 


Sin 

andn 

of  Noj 

glacia 

basis. 

niulga 

tary  h 

ice  loa 

as  sout 

decoiu) 

terrane 


t.'b-t.aiii^ia^! 


BULLETIN  OF  THE  GEOLOGICAL  SOCIETY  OF  AMERICA 
Vol.  1,  pp.  163-174  March  12,  i89o 


y 


NOTE  ON  THE  PRE-PALEOZOIC  SURFACE  OF  THE  ARCHEAN 

TERRANES  OF  CANADA. 


BY  ANDREW  C.  LAWSON,  PH.  D. 


{Read  before  the  Society  December  27,  1889.) 


CONTENTS. 

Pftge 

Introductory  Remarks  ^ 168 

The  Phenomena  in  Central  Canada 164 

Contacts  between  the  Animikie  and  the  Archean 164 

Contacts  between  the  Nipigon  and  Older  Rocks 166 

The  Phenomena  in  Eastern  Canada 167 

Contacts  between  the  Paleozoic  and  the  Archean 167 

Review  of  the  Evidence. 169 

General  Considerations 169 

.  Former  Extension  of  the  Paleozoic 169 

Transgressions  and  Oscillations  in  Level .__  171 

The  Erosion  of  the  Archean 172 

Source  of  Paleozoic  Sediments 172 

Discussion 173 


Introductory  Remarks. 

Since  the  establishment  of  the  glacial  theory  the  cause  of  the  hummocky 
and  rtc/ies  moutonnees  character  of  the  rocky  surface  of  the  Archean  terranes 
of  North  America  has  generally  been  ascribed  to  the  action  of  the  ice  of  the 
glacial  epoch.  Two  opinions  have  been  prevalent,  having  this  belief  as  their 
basis.  The  first  and  older  view  was,  in  accordance  with  the  theories  pro- 
mulgated by  the  Scotch  geologists,  that  the  hummocks  and  their  complemen- 
tary hollows  were  produced  by  the  direct  plowing  or  gouging  action  of  glacier 
ice  loaded  with  rock  debris.  The  second  and  more  modern  view  is,  that  just 
as  south  of  the  terminal  moraine  we  find  the  crystalline  rocks  extensively 
decomposed  in  situ,  so  prior  to  the  advent  of  the  glacial  epoch  the  Archean 
terranes  of  the  north  were  similarly  decomposed,  and  the  present  hummocky 


XXII— Bull.  Geol.  80c.  Am.,  Voi,.  1, 1889. 


(168) 


104 


A.    V.    LAWSOX — THE    PRE-PALKOZOir    STTRPAf'E. 


surface  represents  the  locus  to  wliicli  rock  decay  hiul  exten<le<l  in  depth.  In 
this  view  the  ice  ainjply  removed  the  rotten  rock,  scouring  and  polishing 
the  fresh  surface  upon  which  it  rested,  and  the  humrnoeky  character  is  due 
rather  to  the  principles  which  govern  the  decay  of  rocks  than  to  ice  action, 
which  is  only  held  responsible  for  laying  the  surface  bare.  All  students  of 
glacial  geology  will  concede  that  in  both  of  these  opinions  there  is  a  certain 
amount  of  truth,  though  much  more  in  the  second  than  in  the  first. 

Some  observations,  however,  which  the  writer  has  been  enabled  to  make 
at  odd  times  during  the  past  few  years,  indicate  thstlhese  hypotheses  do  not 
afford  us  the  correct  explanation  of  the  hummocky  aspect  of  the  Archean 
surface,  but  that  the  latter,  in  its  essential  and  prominent  features,  long 
antedates  the  glacial  epoch,  and  was  as  characteristic  of  the  surface  upon 
which  the  earliest  Paleozoic  sediments  were  deposited  as  of  that  upon  which 
the  great  Canadian  glacier  rested  in  glacial  times.  These  observations  have 
been  made  along  the  northern  limit  of  the  undisturbed  Animikie  and  Nipigon 
strata,  where  they  rest  directly  upon  the  Archean  surface,  on  the  north  shore 
of  Lake  Superior,  between  Gunflint  lake  on  the  international  boundary  and 
the  meridian  of  the  Slate  islands.  The  conclusions  which  they  forced  upon 
the  writer  have  been  confirmed  by  an  inquiry  which  he  has  made  into  the 
conditioris  which  prevail  along  the  line  of  contact  of  the  undisturbed  Paleozoic 
rocks  upon  the  Archean  in  more  eastern  portions  of  Canada. 

In  a  paper  of  the  present  compass  it  will  scarcely  be  possible  to  do  more 
than  indicate  the  localities  where  the  evidence  may  be  found,  and  to  sketch 
the  latter  at  each  place  in  scant  outlines. 

The  Phenomena  of  Central  Canada. 

Contacts  between  the  Animikie  and  the  Archean. — On  the  north  side  of 
Gunflint  lake  the  superposition  of  the  northern  edge  of  the  Animikie  upon 
the  Archean  is  well  seen.  To  the  north  of  the  edge  of  the  Animikie  for- 
mations the  Archean  rises  in  low  hummocky  hills,  the  ridges  of  which,  when 
these  are  present,  coincide  with  the  strike  of  the  rocks.  This  hummocky 
surface  may  be  walked  over  close  up  to  the  Animikie,  and  it  may  be  seen  to 
form  an  undulating  surface  upon  which  the  latter  rests.  At  the  west  end  of 
the  lake,  on  the  north  side  of  Black-fly  bay,  on  mining  locations  R.  315  and 
R.  317,  is  an  outlier  of  the  basal  beds  of  the  Animikie  resting  on  a  ridge  of 
Laurentian  gneiss,  with  hollows  on  either  side  of  it,  and  the  Animikie  at 
the  bottom  of  that  on  the  south,  the  whole  showing  very  clearly  that  the 
present  shape  of  the  surface  of  the  Laurentian  was  practically  that  upon 
which  the  Animikie  was  laid  down.  The  direct  repose  of  the  flat 
Animikie  upon  the  upturned  edges  of  the  Keewatin  schists  is  also  observable 
a  mile  and  three-quarters  from  the  east  end  of  the  lake,  and  here  the  surface 


!  ( 


i 


*       ^ 


T 


HUMMOCK Y    AUCHKAN    SUIU-'ACES. 


105 


•<>• 


is  of  the  same  uneven  cliaracter  as  that  of  the  uncovered,  glaciated  country 
to  the  north.  Similar  contacts  may  be  seen  inland  a  short  distance,  near 
the  head  of  the  lake ;  and  on  Gunflint  river  the  Laurentian  gneiss,  in  low 
roches  moutoniues,  ai)[)ear8  jjartially  encircled  by  the  Animikie  rocks. 

On  the  north  side  of  North  lake  there  flows  in  a  creek  at  the  bottom  of  a 
deep  gorge,  which  cuts  down  through  200  feet  of  flat  Animikie  strata  to  the 
basement  of  Laurentian  gneiss  upon  which  they  rest;  and  the  basement  is 
distinctly  roches  rnoutonnres.  Similar  conditions  are  observable  two  miles 
up  the  creek  which  flows  into  the  east  end  of  North  lake,  and  on  Sand  lake, 
where  escarpments  of  Animikie  strata  overlook  and  appear  to  overlie  a  hum- 
mocky  surface  of  Laurentian  gneiss.  The  same  is  true  of  the  escarpments  in 
the  vicinity  of  Little  Gull  lake. 

To  the  north  and  northeast  of  Little  Gull  lake  is  a  group  of  five  small 
steep-sided,  flat-topped  hills,  known  as  the  Outpost  hills,  which  are  outliers 
of  the  Animikie,  capped  as  usual  with  a  sheet  of  columnar  trap.  The  dis- 
tance which  separates  them  from  the  main  area  of  these  rocks  varies  from 
one  to  four  miles.  This  space  is  occupied  by  a  very  hummocky  and  roches 
moutonnees  stretch  of  Laurentian  gneiss  which  maintains  the  general  level 
of  a  line  extending  from  the  base  of  the  Animikie  on  the  face  of  the  escarp- 
ment to  the  base  of  the  same  series,  where  it  rests  on  the  Laurentian  at  the 
foot  of  the  Outpost  hills.  The  writer  has  been  over  the  ground  between  the 
escarpment  and  the  hills ;  and  Mr.  E.  D.  Ingall,  of  the  Geological  Survey 
of  Canada,  who  has  examined  the  hills  carefully,  informs  the  writer  that 
the  actual  base  of  the  Animikie  may  be  distinctly  observed  resting  upon 
the  uneven,  hummocky  Laurentian  surface,  the  sections  being  perfectly  ex- 
posed. 

Less  than  half  a  mile  above  Kakabeka  falls  small  outlying  patches  of  the 
basal  beds  of  the  Animikie  may  be  seen  lying  in  the  hollows  of  the  mam- 
millated  surface  of  the  Laurentian,  and  the  latter,  as  it  rises  from  beneath 
the  Animikie,  above  the  falls,  is  exceedingly  hummocky. 

Along  the  Dawson  road,  a  few  miles  back  of  Port  Arthur,  low,  rounded 
domes  of  Laurentian  gneiss  appear  in  the  midst  of  the  Animikie,  projecting 
above  the  level  of  the  local  upper  beds. 

On  Current  river  the  Laurentian  rises  in  hummocky  hills  from  beneath  the 
Animikie  slates  and  traps,  although  the  actual  contact  has  not  been  observed. 
Between  this  and  McLean's  siding,  seven  miles  east  of  Port  Arthur  on  the 
Canadian  Pacific  railway,  the  Archean  rises  in  the  same  hummocky  hills 
from  beneath  the  Animikie,  the  line  of  contact  being  concealed  by  a  narrow 
strip  of  swamp.  At  the  siding  the  contact  is  only  concealed  by  the  width 
of  the  road-bed,  and  the  surface  of  the  Laurentian  gneiss  is  seen  to  plunge 
down  under  the  flat  Animikie  rocks  with  the  slope  of  a  steep  dome,  appear- 
ing again  in  a  less  prominent  but  still  hummocky  outcrop  close  to  the  con- 


100 


A.    C.    LAWSON — TIIK    I'UK-rALKUZUlC   .SURFACE. 


tact  of  the  Aniinikie,  on  the  wagon  trail  about  midway  between  Green  point 
and  Wihl  Goose  point. 

At  Silver  harbor,  farther  up  the  north  side  of  Thunder  bay,  there  is  a  strip 
of  the  Animikie  consisting  of  lo  to  20  feet  of  flat  slates  and  cherty  beds, 
capped  'y  50  feet  of  trap,  from  beneath  which  on  the  north,  across  a  narrow 
strip  of  swamp,  rises  the  Archean  surface  in  well-defined  roches  moutounees. 

Contacts  between  the  Nipigon  and  Older  Rocks. — In  the  viciuity  of  Loon 
lake  the  basal  beds  of  the  Nij)igou  series  overlapJjie  northern  edge  of  the 
Animikie  and  rest  in  undisturbed  attitudes  directly  upon  the  Laurentian. 
On  the  north  side  of  Loon  lake  and  eastward  to  the  vicinity  of  Pearl  river 
the  Laurentian  rises  from  beneath  the  Nipigon  sandstones  and  conglomerates 
in  prominent  huramocky  hills.  These  conglomerates  are  made  up  very 
largely  of  boulders  and  rounded  pebbles  of  the  Laurentian,  which  are  in- 
distinguishable in  general  aspect  from  the  more  rounded  erratics  in  the 
glacial  drift. 

In  the  bed  of  the  creek  at  the  tank  of  Pearl  river  station  a  low,  rounded 
hummock  of  Laurentian  gneiss  appiears  from  beneath  the  Nipigon  sandstones ; 
and  at  the  first  rock  cut  east  of  the  station,  200  or  300  yards  distant,  the 
sandstones  may  be  seen  in  the  vertical  section  of  the  cutting,  resting  upon 
the  slope  of  a  hummock  of  Archean  schists  and  dipping  away  from  it  to  the 
east  at  an  angle  of  15°.  Here  the  schists  are  rotted  in  places,  leaving  a  few 
harder  nuclei  or  boulders  of  disintegration  in  situ.  Half  a  mile  farther 
east  along  the  track  prominent,  lumpy  knobs  of  Laurentian  rise  above  the 
level  of  the  Nipigon  sandstones  to  a  height  of  over  100  feet,  and  on  the  east 
side  of  these,  in  a  rock  cut  of  the  railway,  the  sandstones  may  be  seen  repos- 
ing directly  upon  their  slopes,  as  an  outlying  patch. 

About  ten  miles  east  of  Nipigon,  on  the  Canadian  Pacific  railway,  there  is  a 
prominent  bluff  of  Nipigon  sandstone,  capped  with  a  thick  sheet  of  verti- 
cally columnar  trap,  the  whole  presenting  escarped  faces  which  rise  on  three 
sides  precipitously  for  several  hundred  feet  above  the  hummocky  plain  of 
Laurentian  rocks  upon  which  it  rests.  The  bare  Laurentian  basement  is 
traceable  up  to  the  talus  at  the  bases  of  the  cliffs,  and  presents  the  appear- 
ance of  passing  under  the  colunni  of  superincumbent  strata  in  the  same 
hummocky  condition  as  that  which  it  has  beyond  the  cliffs. 

About  ten  miles  east  of  Mazokama  station  on  the  Canadian  Pacific  rail- 
way a  prominent  point  runs  out  into  the  lake,  the  core  of  which  consists  of 
hununocky  Laurentian  gneiss,  and  the  outer  margin  or  shore  of  superim- 
posed Nipigon  sandstones  and  conglomerates.  Here  again  the  Laurentian 
appears  to  pass  under  the  Nipigon  with  its  characteristically  hummocky  sur- 
face, the  country  being  well  bared ;  and  that  it  does  so  is  proved  beyond 
question  by  the  fact  that  scattered  over  the  Laurentian  area,  away  from  the 
edge  of  the  Nipigon  rocks,  there  are  numerous  outlying  patches  of  the  basal 


4 


AUCHEAN   .SUUKACI-:    (JNCIIANMiKlJ  HINCK   TJIK   NIPIUON. 


107 


4^ 


beds  of  the  Nipigon  resting  in  situ  in  the  hollows  between  the  Laurcntian 
hummocks,  both  at  the  bottoms  of  the  hollows  and  on  the  steep  slo])e8. 
These  patches  are  usually  not  more  than  a  few  chains  in  diameter ;  and  their 
relation  to  the  Laurentian  affords  incontestable  proof  that  the  surface  of 
the  latter  has  undergone  no  material  change  siiiee  they  were  deposited  upon 
it.  At  Rossport  the  Aniniikie  rocks  come  in  sij^ain  between  the  Archean 
and  the  Nipigon,  and  here  also  may  be  seen,  near  the  railway  station,  in  a 
hollow  between  the  Laurentian  hillocks,  an  outlying  patch  of  the  basal  beds 
of  these  rocks. 

Along  the  shore  of  the  lake  between  liossport  atid  Black  river,  north  of 
the  Slate  islands,  there  are  occasional  patches  of  the  Nipigon  araygdaloidal 
traps  which  have  escaped  removal  by  erosive  agencies,  and  these  all  repose 
upon  a  hjmmocky  Archean  surface.  In  none  of  these  instances  is  there 
any  evidence  of  a  perceptible  reduction  of  the  mean  level  of  the  glaciated 
surface  of  the  Archean  below  that  upon  which  the  Nipigon  or  Aniniikie 
rocks  rest.  A  noteworthy  fact  also  is,  that  with  one  exception  none  of  the 
Archean  rocks,  where  they  pass  immediately  beneath  the  Animikie  or  Nipi- 
gon, show  the  slightest  evidence  of  decay.  On  the  contrary,  they  are 
remarkably  fresh  and  free  from  even  the  incipient  decomposition  of  weather- 
ing. The  exception  is  the  case  of  the  schists  in  the  rock  cut  east  of  Pearl 
river  mentioned  above.  All  the  Laurentian  gneisses  and  granites  are  per- 
fectly fresh  in  their  macroscopic  aspects.  Another  interesting  point,  which 
will  be  alluded  to  again,  is  the  transgression  northward  of  the  newer  Nipigon 
rocks  beyond  the  edge  of  the  older  Animikie. 


The  Phenomena  in  Eastern  Canada.  "     v 

On  instituting  a  comparative  inquiry  into  the  conditions  which  obtain 
along  the  escarped  line  of  the  abutment  of  the  undisturbed  Paleozoic  upon 
the  Archean  in  eastern  Canada,  it  is  found  that  the  evidence  here  confirms 
the  conclusions  arrived  at  on  Lake  Superior  as  to  the  general  character  of 
the  pre-Paleozoic  Archean  surface. 

Contacts  betiveen  the  Paleozoic  and  the  Archean. — Laflamme  in  his  "  report  of 
geological  observations  in  the  Saguenay  region  "  *  seems  to  have  arrived  at 
nmch  the  same  conclusion  as  the  writer.  After  describing  a  new  area  of 
the  Trenton  rocks  in  the  vicinity  of  the  Saguenay  "  which  rest  directly  on  the 
gneiss,"  and  stating  that  "  their  thickness  is  so  slight,  at  least  on  the  border 
of  the  formation,  that  the  undulations  of  the  gneiss  are. brought  to  light 
through  their  edge,"  he  gives  an  account  of  various  outliers  and  says  by  way 
of  summary :  "  I  have  pointed  out  in  the  course  of  these  remarks  the  fact 
that  limestones  (Trenton)  are  often  found  in  nests  or  outliers  amongst  the 

*Geol.  Survey  of  Can»da,  Report  Progress  for  1882-3-4,  Part  D. 


108 


A.    (!.    I-ANVSO.N — TIIK    I'KK-I'ALKOZOIC   HIKFACK. 


^raiiitcH.  Tlieroforc,  thcHC  depresHions  aixl  iiillH  of  riaurentian  imiat  nccc8- 
Harily  have  uxiHted  at  the  bottom  uf  the  I'alcoxoic  ocean  when  the  linieutone 
beds  were  being  depoHited."''* 

Mr.  A.  r.  Low,  of  the  Geoh)jfical  Kurvey  of  (*anada,  who  hau  been  more 
recently  eiij^agcd  in  tracing  ont  the  northern  limitH  of  the  Pahur/oic  on  the 
north  Hide  of  the  St.  Jjawrence,  west  of  {^nel)ec  city,  informs  the  writer  that 
at  Hcveral  phiccH  he  has  noted  the  HnperpoHition  of  the  Trento«i  or  Lorraine 
beds  directly  upon  the  hummocky  Jjaurentian  surface,  and  that  there  has 
been  no  redncticm  of  the  surface  where  it  projects  from  beneath  the  escarp- 
ments, below  that  where  the  tlat  strata  rest  upon  it.  He  notes  the  following 
localities  as  aHbrding  particularly  good  sections : — lietween  Loretto  village 
and  St.  Ambrose  railway  station,  (^.  L.  St.  J.  railway  ;  west  of  Belair  station, 
C.  P.  railway;  Pont  Kouge  station,  C.  P.  railway  (section  on  Jacques  Cartier 
river);  Deschambault,  near  railway  station.  Mr.  Low  also  informs  the 
writer  that  the  undisturbed  limestones  of  Lake  Mistassini,  in  southern  Lab- 
ratlor, may  be  observed  to  rest  upon  hununocky  Laurentian  surfaces;  and 
that  on  the  l^ast-main  coast  of  Hudson's  oay  similar  flat  lying  strata  may 
be  seen  in  the  transverse  section  aftbrded  by  Richmond  gulf,  resting  on  a 
very  hummocky  surface. 

In  eastern  Ontario,  the  best  evidence  we  have  bearing  on  this  (juestion  is 
contained  on  Mr.  E.  Coste's  "  Geological  and  Topographical  Map  of  the 
Madoc  and  Marmora  Mining  District,"  recently  published  by  the  Geological 
Survey  of  Canada.  No  report  accompanies  the  map  as  yet,  but  the  writer 
has  had  the  benefit  of  frequent  conversations  with  Messrs.  Coste,  Ami,  and 
White,  who  were  employed  in  the  field-work  necessary  for  its  construction. 
From  the  map  and  from  the  information  thus  supplied,  it  is  clear  that  in  the 
area  mapped  we  have  a  remarkably  striking  illustration  of  the  superposition 
of  flat,  undisturbed  Paleozoic  strata  (Birdseye  and  Blac'i  River)  upon  a 
very  hummocky  and  mammuillated  Archean  surface.  The  northern  border 
of  the  Paleozoic  is  here  very  irregular  in  outline,  and  beyond  the  limit  of 
the  main  area  there  are  very  nunicrous  outliers  scattered  over  the  country. 
Both  along  the  edge  of  the  escarpment  and  at  the  perii)hery  of  many  of 
the  outliers,  the  flat  strata  may  be  seen  resting  directly  on  the  rounded 
hummocks;  and  these,  out  beyond  the  escarpment,  often  rise  high  above  the 
lower  horizontal  strata.  Many  of  the  outliers,  also,  are  mere  patches  resting 
in  situ  upon  the  steep  slopes  of  these  hummocks.  Many  are  but  a  few 
chains  in  diameter,  and  others  only  a  few  yards.  Further,  there  may  be 
repeatedly  seen  projecting  through  the  upper  surface  of  the  Birdseye  and 
Black  River  formations  rounded  knobs  of  the  Archean,  in  the  shape  of  in- 
liers  well  within  the  Paleozoic  area.     These  are  clearly  the  crests  of  partially 

*  Loc.  cit.,  p.  15. 


4^ 


, 


THK    l'«)I'\r>ATlON'    FOIt    THK    WW.Eo'/JiU'. 


Kin 


iiiicovenMl  huininocks;  and  the  plu'iionienon  is  ho  (ioiiinion  us  to  leave  no 
(loiiht  a8  to  the  character  of  the  undcrlyiiig  Hurf'ace. 


Ukvikw  of  tiif  Evidrnck. 

Thu8,  wherever  careful  observations  have  been  made  as  to  the  nature  of 
the  superposition  of  the  undisturbed  Paleozoic  rocks  upon  the  Archean, 
whether  in  the  Lake  Superior  country,  eastern  Ontario,  (Quebec,  or  Labrador, 
the  evi<lence  points  to  the  same  conclusion,  i.  e.,  that  the  early  Paleozoic  rocks 
were  laid  <l()wn  upon  a  surface  which  did  not  (litter  essentially  from  that  pre- 
sente<l  by  the  exposed  Archean  surface  of  the  present  <lay  upon  which  the 
great  C/anadian  glacier  rested ;  and  that  there  is  no  good  evidence  of  that 
surface  having  undergone  any  material  reduction  in  level,  in  consequence 
of  the  conditions  of  the  glacial  epoch,  either  by  any  plowing  power  some- 
times ascribed  to  glacier  ice,  or  by  the  removal  of  the  products  of  extensive 
rock  decay. 

General  Considehations. 

In  the  foregoing  pages  the  evidence,  although  briefly  sketched,  has  been 
specific,  and  attention  has  been  confined  to  the  immediate  vicinity  of  the 
edge  of  the  Paleozoic  formations.  Let  us  turn  now  to  a  somewhat  broader 
aspect  of  the  question. 

Former  Extension  of  the  Paleozoic. — There  is  excellent  presumptive  evidence 
that  the  greater  part,  if  not  the  whole,  of  the  Canadian  Archean  terranes 
were  at  one  time  covered  by  Paleozoic  strata,  and  the  assumption  so  generally 
made  that  they  have  always  formed  an  upland  region,  serving  as  a  source  of 
supply  for  the  sediments  which  built  up  the  Paleozoic  formations,  appears  to 
be  scarcely  warranted  by  the  facts. 

The  reconnaissance  work  of  the  Geological  Survey  of  Canada,  while  it  has 
only  eftected  an  examination  of  a  number  of  linear  sections  across  the  arms 
of  the  V-shaped  Archean  nucleus,  along  the  various  canoe  routes  which 
traverse  it  from  the  waters  of  the  St.  Lawrence  and  Lake  Winnipeg  systems 
to  the  waters  of  Hudson's  bay,  has  yet  established  the  fact  that  there  are 
basins  and  outliers  of  Paleozoic  rocks  scattered  over  its  surface  which  appear 
to  be  but  the  remnants  of  once  far  wider  spread  formations.  In  the  region 
of  the  Saguenay,  Laflamme*  has  described  various  outliers  of  Trenton  other 
than  the  well  known  one  at  Lake  St.  John,  and  the  distribution  of  these 
shows  clearly  that  this  formation  must  have  extended  for  at  least  150  miles 
north  of  the  St.  Lawrence,  over  what  is  now  for  the  most  part  bare  Archean 
surface,  and  the  probability  is  that  it  extended  much  farther. 

*  Op.  cit.,  pp.  10-15. 


170 


A.    C.    T.AWSOX — THE    PRE-PAI.KOZOIf   SlTRFAf'K. 


^ 


To  the  north  the  explorations  of  MeOuat  and  Low  have  established  the 
existence  of  another  large  and  important  outlier  of  undisturbed  Paleozoic 
rocks  over  100  miles  in  extent,  about  150  miles  beyond  Lake  St.  John,  at 
Lake  Mistassini.  These  rocks  are  chiefly  limestone  in  which  as  yet  no 
fossils  have  been  found,  and  which  are  referred  provisionally  to  the  Cambrian 
from  certain  resemblances  to  the  flat  strata  of  the  east  coast  of  Hudson's 
bay  which  are  supposed  to  be  of  that  age.  Tliese  Ihtter  rocks  occur  along 
the  East-main  coast,  resting  in  undisturbed  attitudes  upon  the  Archean. 
Inland  from  this  coast,  also,  Mr.  Low  found  in  the  drift  which  comes  from 
the  east,  or  the  interior  of  Labrador,  a  limestone  boulder  containing  Silurian 
fossils,  which  indicates  the  presence  of  an  outlying  area  of  such  rocks  in  that 
region.* 

On  the  upper  Ottawa,  in  the  vicinity  of  Pembroke,  we  find  extensive 
Cambro-Silurian  outliers  as  much  as  50  miles  from  the  edge  of  the  present 
main  Paleozoic  basin.  Other  outliers  are  also  found  on  the  islands  of  Lake 
Nipissing,  and  on  Lake  Teniiscaming  nearly  100  miles  north  of  Lake 
Nipissing.  There  is  thus  good  reason  for  supposing  that  the  Paleozoic  seas 
extended  far  over  the  whole  of  the  upper  Ottawa  country. 

The  great  Siluro-Devonian  basin  of  the  west  side  of  James's  bay  extends 
southward  to  within  100  miles  of  the  north  shore  of  Lake  Superior,  and 
farther  west  the  rocks  of  the  Nipigon  basin  extend  northward  for  100  miles. 
The  former  extends  south  and  the  latter  north  of  the  50th  parallel  of  latitude, 
and  the  east  and  west  distance  between  the  two  basins  along  the  parallel  is 
only  about  100  miles.  It  is  entirely  probable  that  both  of  these  basins  only 
represent  what  is  left  by  erosion  of  a  much  more  extensive  distribution  of 
the  respective  formations  constituting  them  ;  and  that  they  do  not  in  reality 
correspond  in  area  to  the  original  basins  of  deposition,  but  are  rather  basins 
of  shelter  from  erosion,  such  as  all  the  Paleozoic  outliers  appear  to  be. 

On  the  southwest  side  of  Hudson's  bay  there  is  another  extensive  area  of 
Silurian  rocks,  traversed  by  the  lower  stretches  of  the  Churchill,  the  Nelson, 
the  Hayes,  and  the  Severn  rivers.  These  rocks  resemble  those  of  the  same 
age  in  the  basin  of  the  Red  river  and  Lake  Winnipeg,  both  as  regards  their 
fossil  remains  and  their  lithological  characters.  The  Hudson's  bay  area  of 
these  rocks  is  separated  from  that  on  Lake  Winnipeg  by  about  200  miles  of 
Archean  country,  with  no  prominent  elevations  between,  and  it  is  therefore 
quite  probable  that  they  were  once  connected,  and  that  the  formations  of 
which  they  are  constituted  extended  continuously  across  this  northwestern 
arm  of  the  V-shaped  Archean  "  nucleus."  An  outlying  area  of  sand- 
stones of  unknown  age  also  rests  upon  the  Archean  at  the  east  end  of 
Athabasca  lake. 

Thus,  considering  the  very  limited  extent  to  which  this  Archean  "  nucleus" 


*  Geol.  Survey  of  Canada,  Annual  Report.  Vol.  Ill,  1887,  Part  J,  p.  59. 


^ 


KOUMKK    EXTKNSIOX   Ol'    TIIK    I'ALKOZOIC. 


171 


' 


has  been  explored,  the  indications  that  it  was  ouce  very  extensively  if  not 
wholly  covered  by  formations  of  Paleozoic  age  are  both  numerous  and  im- 
portant. The  lines  of  examination  have  been  chiefly  confined  to  the 
ordinary  routes  of  travel  followed  by  the  fur  traders,  and  these  are  not 
numerous.  When  the  country  comes  to  be  more  <  losely  explored  there  is 
every  reason  to  suppose  that  niany  other  outliers,  such  as  those  of  lakes  St. 
John,  Mistassini,  Nipissing,  and  Tcrniscaming  and  the  Ottawa  river,  will  be 
found  scattered  over  its  surface,  and  that  the  evidence  of  the  once  wide-spread 
distribution  of  the  Paleozoic  formations  will  accumulate. 

Transgressions  and  Oscillations  in  Level. — But  here  a  word  of  caution  and 
modification  is  necessary.  While  the  evidence  indicates  that  a  covering  of 
Paleozoic  (Cambrian  to  Devonian)  once  spread  over  the  Archean  surface,  it 
does  not  indicate  that  the  rocks  of  the  lower  horizons  were  thus  widely 
spread.  On  the  contrary,  it  is  to  be  noted  that  there  are  distinct  evidences 
of  the  transgression  of  the  formations  of  higher  horizons  over  the  limiting 
edges  of  the  lower.  Thus,  on  Lake  Superior,  the  Nipigon  rocks  may  be  dis- 
tinctly observed  to  overlap  the  northern  edge  of  the  Animikie  fornuition  and 
extend  northward  far  beyond  it.  In  the  St.  Lawrence  and  lower  Ottawa 
region,  rocks  of  Potsdam  and  Calciferous  age  are  abundant.  Further 
north  these  are  absent,  and  in  the  upper  Ottawa  outliers  the  Chazy  rests 
directly  upon  the  gneiss.  In  the  vicinity  of  Madoc  this  also  is  lacking,  and 
the  Birdseye  and  Black  River  beds  rest  directly  upon  the  gneiss.  This 
appears  to  be  true  also  of  the  outliers  on  Lake  Nipissing.  Thus,  in  ascend- 
ing the  Ottawa,  the  Cliazy  overlaps  or  transgresses  both  Potsdam  and  Calcif- 
erous, while  at  Madoc  and  Nipissing  all  of  these  are  transgressed  by  the 
Birdseye  and  Black  River.  This,  in  turn,  and  all  older  formations,  were 
transgressed  by  the  Niagara,  as  is  indicated  by  beds  of  that  age  resting 
directly  on  the  Archean  on  Lake  Temiscamany. 

In  the  Province  of  Quebec  the  same  condition  of  affairs  is  found. 
In  the  vicinity  of  the  St.  Lawrence,  the  Ciiazy  and  Calciferous  rocks 
abound.  To  the  north  of  this,  in  the  Snguenay  country,  LaHamme  remarks 
as  a  noteworthy  fact,  that  in  all  the  points  of  contact  which  ne  has  been 
able  to  observe  between  the  Laurentian  and  the  Trenton,  the  latter  rests 
directly  upon  the  former,  no  traces  of  Potsdam,  Calciferous,  or  Chazy  being 
seen.  Moreover,  whilst  the  Utica  formation  is  present  only  in  a  few  instances, 
still  debris  from  it  are  found  on  the  shores  of  tiie  lake  (St.  John),  and  very 
often  inland  to  such  an  extent  that  we  are  forced  to  conclude  that  the  whole 
area  of  the  Trenton  was  formerly  covered  with  this  fornuition. 

Thus,  while  the  evidence  indicates  that  the  Archean  "  nucleus"  was  once 
covered  very  extensively  by  Paleozoic  formations  of  one  horizon  or  another, 
it  appears  ])robable  that  it  was  not  extensively  submerged  till  the  time  of 
the  Trenton,  and  that  it  was  much  more  extensively  submerged  during  the 

XXIII— Bum..  Geoi,.  Sue.  A.ti.,  Voi,.  1, 18«!). 


1 


72 


A.    C.    [,AWS<>\ — THK    l'l!i:-l'AI,KOZo|C    SIIU'ACK. 


deposition  of  the  Niagara  than  in  earlier  epochs.  It  would  follow  from 
these  considerations,  that  as  Paleozoic  time  advanced  from  Cambrian  to  late 
Silurian  or  Devonian  there  was  a  gradual  and  progressive  subsidence  of  this 
portion  of  the  continent.  As  we  have  no  evidence  of  the  deposition  of  post- 
Devonian  formations  anywhere  over  the  Archean  "  nucleus  "  till  we  come 
down  to  post-Tertiary,  it  may  be  tentatively  inferred  that  after  the  Devonian 
it  was  again  elevated,  and  this  elevation  proBably  only  reached  its  maximum 
during  the  glacial  epoch,  affording  the  conditions  of  altitude  contended  for 
by  nmny  writers  to  explain  the  great  precipitation  of  snow.  In  post-glacial 
tinjes  we  know  from  the  distribution  of  such  formations  as  the  Leda  day 
and  Saxieava  sand  that  the  northern  part  of  the  continent  was  again  par- 
tially submerged  for  several  hundred  feet,  from  which  depression  it  has  since 
recovered  ;  we  thus  have  evidence  of  a  slow  vertical  pulsation  of  the  surface 
of  this  part  of  the  continent,  of  which  there  have  been  at  least  four  great 
beats  since  early  Cambrian  times. 

But  this  is  a  digression,  and  the  argument  which  has  led  to  these  remarks 
was  inaugurated  to  show  simply  that  the  surface  of  the  Archean  "  nucleus  " 
was  once  very  extensively  if  not  wholly  covered  by  Paleozoic  sediments. 
This  covering  probably  accounts  in  a  large  measure  for  the  remarkable 
])reservation  of  the  Archean  surface  in  the  condition  in  which  pre-Paleozoic 
denudation  left  it.  There  are  other  considerations  which  help  us  to  under- 
stand this  preservation,  such  as  the  levelness  of  the  plateau  and  its  compari- 
tively  low  altitude,  combined  with  the  very  resistant  character  of  most  of 
its  rocks,  which  appear  to  be  little  susceptible  to  that  erosive  or  corrasive 
action  of  streams  which  is  so  effective  in  removing  the  more  yielding  strata 
of  post-Archean  age.  These  considerations  will  not,  however,  be  entered 
upon  here. 

The  Erosion  of  the  Archean. — One  is  constantly  impressed  by  the  perfectly 
appalling  amount  of  denudation  to  which  the  Archean  has  been  subjected  in 
order  to  truncate  its  formations  down  to  the  surface  which  it  presents  to-day. 
And  when  we  reflect,  as  a  result  of  the  conclusions  here  arrived  at,  that  this 
denudation  was  practically  completed  before  the  beginning  of  earliest 
Paleozoic  times,  and  has  not  been,  as  commonly  supposed,  the  result  of  later 
agencies,  there  looms  up  a  conception  of  the  pre-Paleozoic  interval  necessary 
for  such  denudation  which  staggers  even  the  most  stalwart  geological 
imagination.  To  say  that  it  must  have  been  comparable  with  all  the  time 
which  has  succeeded  from  the  earliest  Cambrian  to  the  present  seems  but  a 
feeble  way  of  expressing  it. 

/Source  of  Paleozoic  Sediments. — The  conce})tion  of  a  covering  of  Paleozoic 
strata  over  the  surface  of  the  Archean  '*  nucleus,"  which  probably  endured 
into  comparatively  recent  geological  times,  enables  us  to  a  large  extent  to 
understand  the  preservation  of  the  pre-Paleozoic  surface,  but  it  also  raises  the 


SOIIJCK    OF'    PA rj<;( )/<>[(•    SKDIMKNTS. 


1—0 


f 


important  question  of  the  source  of  the  sediments  composing  those  strata. 
If  such  a  wide-spread  formation  as  the  rocks  of  Niagara  age  was  deposited 
over  the  surface  of  the  Archean  "  nucleus,"  as  well  as  over  the  regions  which 
encircle  it,  it  is  clear  that  the  Archean  "  nucleus  "  could  not  have  been  the 
source  of  supply  of  those  sediments.  Some  other  portion  of  the  continent, 
or  some  other  region  now  submerged,  must  have  constituted  the  dry  land  of 
that  time.     Where  that  region  lies  is  a  question  yet  to  be  answered. 

DISCUSSION. 

Professor  J.  \V.  Spencer  :  The  facts  set  forth  in  this  very  interesting 
paper  by  Dr.  Lawson  have  their  counterparts  in  the  geological  structure  of 
the  South.  The  hummocky  and  rounded  rock  surfaces  have  always  had  an 
interest  for  me,  on  account  of  their  common  occurrence  in  regions  which 
have  been  glaciated,  and  hence  regarded  by  many  as  evidence  of  glacial 
erosion.  But  in  the  paper  of  Dr.  Lawson  we  learn  that  such  surfaces  existed 
before  the  formation  of  the  early  Paleozoic  terranes.  Some  of  you  may  be 
familiar  with  Stone  Mountain,  about  fifteen  miles  from  Atlanta,  Georgia. 
This  is  a  rounded  granite  hummock  of  over  a  mile,  in  longer  diameter,  rising 
700  feet  above  the  plain.  The  rock  is  remarkably  free  from  joints,  and  is 
rarely  traversed  by  even  an  insignificant  vein.  Thus  its  structure  has  been 
favorable  to  the  preservation  of  the  rounded  form,  whose  outline  is  as  perfect 
as  any  of  the  domes  of  glaciated  Norway  or  Canada ;  or  of  southeastern 
Missouri,  which  lies  outside  of  former  glacial  action.  Stone  Mountain  rises 
from  beneath  very  much  disturbed  strata  of  gneiss,  whose  beds  dip  to  the 
southeast,  and  there  is  no  gradation  of  any  importance  between  the  granite 
and  the  gneiss.  The  gneiss  is  decayed  to  a  depth,  in  some  places,  of  at  least 
sixty  feet ;  but  the  granite  is  compact,  without  being  weakened  by  even 
incipient  decay.  The  surface  materials,  as  fast  as  decomposed,  are  washed 
off  by  the  rains.  Thus  the  contrast  between  the  two  formations  of  rocks  is 
preserved.  This  Stone  Mountain  is  only  one  of  many  in  Georgia  and  Ala- 
bama. Here,  then,  we  have,  in  the  South,  pre-Paleozoic  surfaces  as  old  as 
or  older  than  those  described  by  Dr.  Lawson  in  the  Lake  Superior  region, 
and  brought  to  light  by  simple  atmospheric  action.  Along  the  Potomac 
river  we  find  hummocks  being  formed  by  the  progress  of  atmospheric  in- 
vasion along  lines  of  joints,  but  these  are  now  in  process  of  formation,  and 
do  not  represent  so  ancient  surfaces  as  those  of  the  granite  hummocks  of 
the  South. 


BULLETIN   OP  THE   GEOLOGICAL  SOCIETY  OF  AMERICA 
Vol.  1,  pp.  175-194  March  20,  i890 


THE  INTERNAL  RELATIONS  AND  TAXONOMY  OF  THE 
ARCHEAN  OF  CENTRAL  CANADA. 

BY   ANDREW   C.    LAWSON,   PH.  D. 

(Read  before  the  Society  December '2S,  \SS9.) 

CONTENTS. 

Page. 

Primary  Separation  of  the  Archean  into  two  Divisions 176 

The  Upper  Division 176 

Nomenclature ]7<» 

Petrographical  Description 177 

Original  Characters  and  Metamorphism 180 

Relations  between  the  two  Divisions 181 

The  General  Relations 181 

Irruptive  Contact  on  L"    -i  of  the  Woods 182 

Irruptive  Contact  in  Rainy  Lake  Region 18.S 

■    Significance  of  Relationship 186 

Principles  of  Classification ...    180 

Principles  applicable  to  the  Upper  Division 18f! 

Principles  applicable  to  the  Lower  Division 186 

Diflxjrent  Generations  of  Laurentian  Rocks 187 

Other  Conditions  considered 187 

Similar  Observations  elsewhere 188 

Geognostical  Equivalents  of  the  Archean 190 

The  Argument  from  Analogy 193 


Primary  Separation  of  the  Archean  into  two  Divisions. 

Throughout  North  America,  geologists  have  long  recognized  in  the  great 
fundamental  complex  of  rocks,  known  generally  to-day  as  the  Archean,  a 
natural  division  into  two  well-characterized  portions,  related  to  each  other 
in  space  as  upper  and  lower.  The  lower  division  is  commonly  known  as 
the  Laurentian,  and  consists  for  the  most  part  of  an  assemblage  of  rocks  of 
the  character  of  granites,  syenites,  diorites,  and  gabbros  in  mineralogical 
composition,  but  more  or  less  foliated  or  gneissic.  Involved  with  these  in  a 
way  not  hitherto  understood  there  are  also,  in  some  regions,  portions  of 


17(5 


A.  C.  [;A\VS(>\ — UKr.ATFoNS  OK  TIIK  AI.MIflCAN  ol'  CANADA. 


various  j^neisH,  schist,  limestone,  (jiiartzite,  and  c<Migloinerate  formations, 
whicli,  not  being  easily  separable  from  the  foliated  granite  rocks,  have  been 
sometimes  classed  with  the  latter  as  Laurentian. 

The  Uri'Eii  DrvisroN. 

Nomendaturc. — The  upper  division  is  of  very  varied  lithological  character, 
and  various  names  have  been  applied  to  it,  or  to  portions  of  it,  in  different 
regions.  Until  recently  it  has  been  customary  to  apply  the  term  Huronian 
to  a  part  of  this  upper  division  on  account  of  its  supposed  et^uivalence  to  the 
series  of  rocks  so  named  by  Logan  and  Hunt  in  1855.''^  But  if  the  original 
conceptions  of  these  eminent  geologists  and  the  more  recent  contentions  of 
Irving,  corroborated  by  Professors  N.  H.  Winchell  and  A.  Winchell,  are 
correct — viz.,  that  the  Huronian  and  Animikie  are  geologically  equivalent, — 
then  we  cannot  in  reason  perpetuate  the  incongruity  of  applying  the  same 
name  to  two  groups  of  rocks  which  lie  one  on  either  side  of  probably  the 
greatest  hiatus  in  American  geological  history.  The  term  Huronian  must 
be  retained  for  the  group  of  rocks  on  Lake  Huron  first  so  named  and  its 
equivalents ;  and,  in  view  of  the  evidence  which  has  been  adduced  of  the 
unconformable  superposition  of  that  group  upon  the  Archeaii  and  its  prob- 
able equivalence  with  the  Animikie,  which  rests  upon  the  Archean  in  glaring 
unconformity,  it  seems  inappropriate  at  present  to  apply  the  terra  Huronian 
to  any  portion  of  the  Archean.  We  are  thus,  at  the  outset  of  any  inquiry 
into  the  Archean,  hampered  by  the  lack  of  an  acceptable  designation  for 
the  great  system  of  rocks  which  constitutes  its  upper  division.  Even  if  the 
Huronian  group  be  demonstrated  to  lie  upon  the  remote  side  of  the  great 
post-Archean  hiatus,  it  would  then  be  only  one  of  several  groups  that  go  to 
form  the  system  which  constitutes  the  upper  division  of  the  Archean  com- 
plex, and  the  system  itself  would  still  be  nameless.  At  least  one  other  great 
group  of  rocks — the  Coutchicliing  (possibly  the  equivalent  of  the  Montalban 
of  Hitchcock) — has  been  brought  to  light,  which  is  not  second  in  taxouomic 
importance  to  the  various  belts  of  rocks  similar  to  the  Keewatin,  which  have 
been  correlated  with  the  Huronian.  So,  granting  that  the  Huronian  shall 
<me  day  hold  an  unchallenged  position  in  Archean  taxonomy,  it  will  not 
have  a  higher  rank  than  that  of  a  grouj).! 

*  A  Sketch  of  tlie  Geology  of  Canadfl,  serving  to  explain  the  Geohigical  Map  and  the  Collection  of 
Economic  iMinerals  sent  to  the  Universal  Exhibition  at  Paris,  1855,  by  VV.  E.  Logan  and  T.  Sterry 


Hunt;  in  Canada  at  the  Universal  Exhibition  of  1855,  p.  415  et  sen. 

term  lliironian  is  first  defined,  the  rocks  now  known  as  the  Animikie  and  iS'ipigon  i<eries  are  taken 


In  this  sketch,  in  which  the 
es  are  taken 
Huronian  or 


together  as  the  equivalent  of  rocks  on  fjake  Huron,  and  the  whc)l«  is  called  the 
Cambrian  system,"  which  is  stated  to  rest  iinconformably  upon  the  Laurentian. 

t  in  this  paper  the  terms  "  system  "  and  "  group  "  have  the  significance  assigned  to  them  by  the 
United  Stales  Geological  Survey,  in  the  scheme  put)lished  in  the  Second  Annual  Report,  l880-'bl, 
p.  xlviii.  The  writer  recognizes,  however,  two  great  "systems"  in  the  Arcliean  complex.  The 
terms  may  later  be  transposed  or  otherwise  changed  to  accord  with  any  general  decision  of  the 
International  Geological  Congress  as  to  usage. 


,. 


.  i 


<      \ 


TlIK    UXTA15IAN    SYSTK.M     I'KOl'OSKD. 


1 


I  t 


Having  these  considerations  in  mind,  it  seems  desirable,  in  the  cause  of  the 
concise  expression  of  our  knowledge  and  of  the  furtherance  of  clear  and 
simple  conceptions  of  Archeau  geology,  that  the  taxonomic  value  of  this 
upper  division  of  the  Archean  should  be  recognized  by  the  adoption  of  an 
appropriate  designation  of  systemic  import.  There  is  probably  no  other 
e(iual  area  of  the  earth's  surface  where  the  formations  of  this  system  are 
better  or  more  extensively  exposed  than  in  the  Canadian  province  of  Ontario. 
The  writer  therefore  begs  to  suggest  to  his  fellow-workers  in  American 
Archean  geology  that  this  system  be  known  as  the  Ontarlan  System. 

Pefroffraphical  Description. — The  formations  of  different  groups  of  the 
Outarian  system  present  for  the  most  part  a  sharp  contrast  in  lithological 
character  and  mode  of  occurrence  to  those  of  the  Laurentiau  system.  The 
latter,  as  has  been  indicated,  consists  essentially  of  an  assemblage  of  more 
or  less  foliated  or  quite  massive  varieties  of  rocks  which  are  to-day  recognized 
by  petrographers  as  plutonic  igneous  rocks — e.  g.,  granites,  syenites,  diorites , 
gabbros,  etc.  The  former  is  composed  of  rocks  which  are  with  varying 
degrees  of  certainty  recognized  as  normal  sedimentary  and  volcanic  forma- 
tions disguised  by  metamorphism  of  different  kinds.  Among  the  more  easily 
recognizable  formations  may  be  mentioned  conglomerates,  grits,  quartzites, 
graywackes,  clay  slates  and  limestones ;  various  pyroclastic  rocks,  such  as 
ashes,  tuffs  and  agglomerates ;  and  massive  volcanic  rocks,  both  acid  and 
basic,  notably  quartz-porphyries  and  diabases  ;  all  of  which  rocks,  far  from 
being  peculiar  to  the  Archean,  are  normal  constituents  of  Paleozoic  and 
later  geological  systems.  In  all  of  these,  schistosity  may  be  a  feature  of  the 
rock. 

With  these  normal  or  only  slightly  altered  rocks  occur  also  more  highly 
altered  facies  of  the  same  formations,  whose  derivation  is  known,  and  others 
still  more  differentiated  from  unaltered  types,  whose  historical  derivation 
from  normal  rocks  cannot  be  traced  with  certainty,  but  only  inferred  by 
analogy  as  highly  probable.  Of  those  rocks  whose  original  character  is 
more  or  less  obscured,  the  most  prominent  are  certain  i)hyllites,  mica  schists 
and  feldspathic  mica  schists  or  gneisses,  so  called  ;  hornblende  schists  and 
amphibolites,  serpentines,  soft,  dark,  glossy,  green  schists,  and  various  light- 
colored  acid  porphyroid  schists,  nacreous  sericitic  schists  and  felsitic  schists 
with  quartz  grains.  These  are  all  rocks  upon  which  there  has,  in  recent 
years,  been  concentrated  a  great  amount  of  research  both  in  the  field  and  in  the 
laboratory,  and  many  facts  have  been  established  concerning  them  in  various 
[)arts  of  the  world  which  enable  us  to  formulate  definite  and  well-grounded 
conceptions  as  to  their  origin  and  development,  where  formerly  only  more 
or  less  indefinite  speculation  was  possible. 

The  rocks  known  as  phyllites  or  phyllitic  schists  are  very  common  in  fos- 
siliferous  series  in  disturbed  regions,  and  their  clastic  origin  is  rarely  (pies- 


178 


A,  C.  I.AWSUX — UKLATIUN.S  OF  TllK  AIUIIKAN  OF  CANADA. 


tinned.  lu  the  Archean,  rocks  of  this  and  more  pronounced  micaceous 
character  to  true  mica  schists  are  traceable  into  clay  slates  and  siliceous 
clastic  rocks  with  unobscured  original  characters.  Other  mica  schists  are 
directly  traceable  into  conglomerates  and  agglomerates,  and  appear  to  be 
but  excessively  8queeze<l  facies  of  these  rocks  where  the  conglomeratic  or 
agglomeratic  characters  have  been  obliterated  and  much  mica  developed. 
And  in  some  mica  schists,  where  no  direct  transition  can  be  established,  traces 
of  conglomeratic  structure  can  occasionally  be  detected.  The  most  distinctly 
crystalline  of  these  mica  schists  are  entirely  comparable  with  the  mica  schists 
of  the  Bergen  peninsula  in  Norway,  where  Reusch  a  few  years  ago  found 
beautiful  Silurian  fossils,*  some  of  which  the  writer  has  himself  more  recently 
collected  under  the  guidance  of  that  distinguished  geologist. 

Many  mica  schists  of  the  Ontarian  system  are,  further,  entirely  similar  to 
the  "hornfels"  or  crystalline  schists  of  the  contact  zones  of  various  post- 
Archean  granitic  irruj)tions,  which  are  undoubtedly  the  altered  facies  of 
normal  sediments.  Some  of  the  feldspathic  mica  schists,  of  a  fine-grained, 
thinly  laminated  aspect,  commonly  called  gneisses,  are  in  parts  of  the 
Ontarian  system  traceable  into  quartz-porphyries  of  the  same  normal 
character  as  those  which  constitute  the  volcanic  portions  of  many  Paleozoic 
series.  The  researches  of  Lehmannf  have  established  such  transformations 
as  facts,  the  explanation  of  which,  as  demonstrated  by  that  eminent  investi- 
gator and  now  generally  accepted,  is  found  in  the  deformation  of  the  rock  by 
pressure  and  in  the  chemical  activity  induced  thereby.  For  the  most  part, 
however,  the  feldspathic  mica  schists,  such  as  are  abundant  in  the  Coutchich- 
ing  group,  are,  like  the  non-feldspathic  mica  schists  associated  with  them, 
very  probably  of  metamorphic  derivation  from  normal  sediments. 

In  portions  of  these  formations  the  writer  has  recently  detected  vestiges  of 
conglomeratic  structure.  In  places  they  pass  into  rocks  that  are  little  more 
than  slightly  micaceous  quartzites,  and  their  distinct  bedding  and  regular 
stratigraphy  are  those  of  sedimentary  rocks  as  contrasted  with  the  lenticular 
arrangements  which  obtain  in  volcanic  accumulations.  Their  contact  phe- 
nomena against  the  granites  and  granite-gneisses  of  the  Laurentianare 
identical,  so  far  as  studied,  with  intrusive  granites,  particularly  in  the 
development  of  andalusite  crystals.  They  correspond  closely  in  lithological 
character  and  in  the  nature  of  their  relations  to  the  Laurentian  with  the 
descriptions  given  us  by  Barrois  J  of  the  feldspathic  mica  schists  of  Cambrian 
age,  which  in  Brittany  are  pierced  and  altered  by  great  irruptions  of  granu- 
lite  (the  true  granite,  or  granite  with  two  micas,  of  the  Germans),  which 
rock  forms  very  extensive  portions  of  the  Laurentian  northwest  of  Lake 
Superior. 


*  Die  Fossilien  Fiihrenden  Kryst.  Sehiefer  von  Bergen.    Leipsic,  1883. 
+  Entst^liiinf?  (ler  Altkrys.  Hchieferge.wt.     Bonn,  1884. 

t<'omptes  Rendtis  des  Excursions  de  la  Soc.  Geol.  de  France  dans  le  Finistere.    Bull.,  3me  S6rie, 
t.  XIV,  1S8G,  p.  832,  et  seq. 


A. 

nicaceoua 
I  siliceous 
jhista  are 
)ear  to  be 
tieratic  or 
ieveloped. 
hed, traces 
t  distinctly 
oica  schists 
ago  found 
)re  recently 

|r  similar  to 
irious  post- 
jd  facies  of 
ine-grained, 
.arts  of  the 
,me  normal 
ly  Paleozoic 
isformations 
lent  investi- 
■  the  rock  by 
\e  most  part, 
le  Coutchich- 
1  with  them, 

ts. 

ed  vestiges  of 

re  little  more 

and  regular 
the  lenticular 

contact  phe- 
aurentian  are 
ularly  in  the 
in  lithological 
tian  with  the 
s  of  Cambrian 
tionsof  granu- 
rmans),  which 
hwest  of  Lake 


STrU'CTIliK    AND    DMItrVATION    OK    TTIK    IJOC'KS. 


170 


J.    Bull.,  3me  S6rie, 


As  to  the  hornblende  schists,  the  field  evidence  ))oint8  to  their  derivation 
from  basic  volcanic  rocks.  In  places  this  derivation  can  be  traced  step  by 
step  from  the  massive  rock  to  the  schist ;  but  for  the  most  part  no  such 
transition  is  observable,  and  at  the  base  erf  the  Keewatin,  in  contact 
with  the  Laurentian,  there  is  commonly  found  a  formation  of  hornblende 
schists  of  whose  origin  and  development  we  can  only  judge  by  comparison 
with  cases  where  the  history  of  similar  rocks  has  been  thoroughly  worked 
out  and  established  beyond  question.  Teall,*  in  Scotland,  and  Reusch,t  in 
Norway,  have  shown  that  some  typical  hornblende  schists  and  more  chloritic 
hornblende  schists  may  be  produced  by  the  shearing  of  diabase  dikes.  The 
writer  has  collected  specimens  of  the  crushed  and  squeezed  diabase  dikes  of 
Bommelo  described  by  Reusch,  which  are  indistinguishable  from  many  of 
the  schists  of  the  Keewatin  on  the  Lake  of  the  Woods  and  Rainy  lake. 
Teall's  description  of  the  hornblende  schists  resulting  from  the  shearing  of 
dikes  would  also  apply  to  many  of  the  Keewatin  schists  which  occur  in  bedded 
formations.  The  augite-porphyrites  of  the  Silurian  of  the  southeast  coast 
of  Norway,  which  have  been  describetl  by  Br6gger,J  are,  at  the  contact  with 
the  intrusion  of  the  augite-syenite  of  Langesundfjord,  where  observed  by 
the  writer,  altered  in  places  into  black  glistening  hornblende  schists,  which 
are  very  similar  to  the  hornblende  schists  of  the  Keewatin  at  its  contact 
with  the  Laurentian  gneisses.  Thus,  both  the  conclusions  arrived  at  in  the 
field  and  supported  by  microscopic  studies,  and  the  analogies  furnished  by  the 
investigations  of  geologists  elsewhere,  point  to  the  derivation  of  the  bulk  of 
the  hornblende  schists  from  normal  volcanic  massive  rocks,  which  were  orig- 
inally bedded  with  other  stratified  rocks,  either  as  flows  or  as  injected  sills. 
Other  hornblende  schists  are  probably  derived  from  an  analogous  alteration 
of  tuffs  of  basic  volcanic  rocks. 

The  amphibolites  are  rocks  very  analogous  to  the  hornblende  schists  in 
mineralogical  composition,  but  massive  or  non-schistose  in  structure.  They 
have  probably  undergone  the  same  chemical  development  as  the  schists, 
with  pressures  so  adjusted  that  no  foliation  was  induced.  They  are  compar- 
atively local  in  their  occurrence  and  do  not  generally  make  extensive  for- 
mations. 

The  various  serpentines,  so  far  as  they  are  known,  are  for  the  most  part 
beyond  doubt  the  alteration  products  of  local  bosses  of  highly  magnesian, 
massive  irruptive  rocks.  This  conclusion  is  based  not  simply  upon  the 
investigation  of  the  rocks  of  this  particular  field  by  the  writer,  but  upon 
the  numerous  instances  that  might  be  cited  from  the  petrographical  writings 


*Mptamorphosis  of  Dolerile  into  Hornblende-Schist;  Quart.  .Tour.  Oeol.  Soc,  Vol.  XFil,  May, 
188f.,  p.  133. 

+  Koinmelrier.  og  Karmoen  med  omgiveJHer  geologisli  beskrevne,  1888,  pp.  M2-:in7. 

iSpaitenverwerfungeninderCiegend  liiingesund:  Nyt  Maga/.in  for  Nuturvidenskaberne,  XXV [I I 
Hind,  3die— 4de  Hefte,  p.  3')2. 

XXIV-Bn.r,.  ftpoi,.  Mo..  Am.,  Voi,.  1,  18Si). 


180 


A.  (\  r.AW80N — UKLATIONH  OF  TIIK  AIMllKAN  OF  CANAOA. 


of  recent  years,  estnblishinj,'  such  an  origin  lor  the  hulk  of  the  serpentines 
at  present  known  the  worhl  over. 

There  ia  a  great  variety  of  fissik!,  more  or  U'ss  ghwsy,  rather  soft,  green 
schists,  partly  hornhIen<li(;  and  partly  chloritic,  the  origin  of  which  in  some 
cases  is  closely  fixed  from  the  fact  that  they  form  the  matrix  of  well  char- 
acterized pehhle  and  howlder  conglomerates.  In  this  case  they  must  have 
been  composed  of  epiclastic  or  pyrochustic  material.  The  writer  inclines  to 
the  opinion  that  they  are  of  proximately  pyroclastic  origin  from  the  fact 
that  precisely  similar  schists,  free  of  j)el)bles,  are  frequently  associated  with 
massive  or  only  slightly  schistose  diabases,  as  if  the  tuffs  of  these  extravasa- 
tions. There  are  many  other  bedded  green  schists  some  of  which  can  be 
shown  to  be  squeezed  and  otherwise  altered  facies  of  diabase,  while  the 
precise  origin  of  others  is  yet  quite  obscure. 

The  porphyroid  schists,  the  felsite  schists  with  quartz  grains,  and  many 
of  the  nacreous  sericite  schists,  represent  stjueezed,  schistose  and  otherwise 
altered  forms  of  quartz-porphyries  and  petrographically  allied  rocks,  and 
their  tuffs,  which,  as  before  stated,  enter  not  uncommonly  into  the  composition 
of  the  volcanic  portions  of  normal  Paleozoic  series.  Some  others  of  the 
sericitic  schists  may  probably  have  been  developed  from  sediments  rich  in 
orthoclase  debris ;  but  this,  except  where  they  pass  over  into  rocks  of  the 
character  of  phyllites,  is  not  so  easily  established  as  the  direct  derivation  of 
many  of  them  from  the  acid  volcanic  rocks.  ^ 

Original  Characters  and  Metamorphism. — From  the  foregoing  statement, 
brief  and  incomplete  as  it  is,  of  the  broad  lithological  characters  of  the  forma- 
tions which  constitute  the  Ontarian  system,  or  upper  division  of  the  Archean, 
it  must  be  apparent  that,  although  there  are  rocks  within  it  whose  history  is 
more  or  less  obscured  by  the  changes  which  they  have  undergone,  the  system 
is  an  assemblage  of  once  normal  rocks,  all  of  which  may  be  found  even  in 
their  most  altered  phases  in  series  of  Paleozoic  and  later  ages.  This  conclu- 
sion will  not  appear  startlingly  new  to  the  very  powerful  school  of  American 
geologists,  who  have  always  claimed  the  metamorphic  derivati(m  of  the  whole 
of  the  Archean  from  normal  rocks. 

But,  as  will  appear  in  the  sequel,  the  metamorphic  explanation  of  the 
whole  of  Archean  phenomena  is  not  tenable,  and  is  only  applicable,  in  the 
opinion  of  the  writer,  to  its  upper  division,  here  designated  the  Ontarian 
system.  Moreover,  it  is  to  be  noted  that  the  conclusion  in(]uestion  offers  an 
important  modification  of  the  old  view  of  the  metamorphic  development  of 
such  rocks  as  constitute  this  system,  inasmuch  as  volcanic  formations  have 
scarcely  been  recognized  in  our  leading  American  text-books  as  having  a 
share  in  the  composition  of  the  older  rock  series.  Much  of  the  Archean  was 
properly  recognized  as  the  alteration  products  of  sediments,  and  the  whole 
complex  was  therefore  inferred  or  supposed  to  be  of  similar  <lerivation  from 


I    ^ 


■ 


'(/ 


DISTINCT   oUKilN    ol'    TIIK    TWO    DIVISIONS. 


181 


Mediineiits.  It  ia  only  in  very  recent  yoiirH  that  the  poHsibility  of  the  deriva- 
tion of  a  portion  of  the  schiats  of  the  Arehean  from  volcanic  rocks  has  been 
looked  into  and  the  important  role  played  by  volcanic  agencies  in  building 
up  the  older  rock  series  has  been  appreciated.-'-  There  are,  however,  not  a 
few  geologists  who  continue  to  advocate  the  extreme  plutonic  view  that  the 
whole  of  the  Archean  is  of  igneous  origin  and  represents  the  first-formed 
crust  of  the  earth.  Hunt's  creuitic  hypothesis,  also,  is  a  challenge  to  the 
metamorphic  theory. 

In  deference  to  these  and  other  anti-metamorphic  schools  of  thought,  in 
which  for  the  most  part  theory  seems  to  crowd  out  fact,  it  becomes  necessary, 
with  the  accumulation  of  evidence  of  recent  years,  to  point  out  the  great 
additional  strength  acquired  by  the  theory  of  metumorphism  as  applied  to 
the  Archean,  by  the  recognition  of  the  volcanic  origin  of  nuich  of  the  material 
upon  which  metamorphic  agencies  have  operated,  and  by  the  limitation  of 
its  application  to  the  upper  division  of  the  Archean  ;  the  rocks  of  the  lower 
division,  or  Laurentian,  being  susceptible  of  an  entirely  different  explanation. 
The  lack  of  discrimination  between  theesseutially  different  characters  of  the 
upper  and  lower  Archean  and  the  lumping  of  the  whole  complex  together  as 
having  necessarily  the  same  origin  and  development  has  been  the  great 
mistake  alike  of  the  metamorphic  and  the  extreme  plutonic  schools.  Just 
as  the  metamorphic  theory,  properly  limited,  affords  the  explanation  of  the 
development  of  the  rocks  of  the  upper  Archean  from  normal  formations,  so 
by  a  similar  limitation  of  the  plutonic  theory  and  the  introduction  of  some 
modifying  considerations  we  will  find  in  the  latter  a  rational  and  consistent 
explanation  of  the  origin  of  the  rocks  of  the  Laurentian. 

Relations  between  the  two  Divisions. 


I 


The  General  Relations. — The  full  significance  of  the  sharp  separation  of 
the  Ontarian  systeni,  as  a  be<lded  assemblage  of  prevailingly  schistose  and 
otherwise  altered  normal  rocks,  from  the  Laurentian,  as  a  non-bedded  assem- 
blage of  more  or  less  foliated  i)lutonic  igneous  rocks,  will  appear  from  an 
inquiry  into  the  relations  in  sj)Hce  and  iu  time  between  these  two  great  sys- 
tems, which  it  is  the  object  of  this  paper  to  institute. 

That  portion  of  the  Ontarian  system  which  for  some  years  has  been  some- 
what loosely  referrc<l  to  as  Huronian,  from  its  supposed  equivalence  with  the 
rocks  of  Lake  Huron,  now  held  to  be  possibly  post- Archean,  presents  in 
many  parts  of  central  Canada  contacts  or  lines  of  junction  with  the  Lau- 
rentian. The  nature  of  this  contact  has  been  a  subject  of  discussion.  The 
question  has  ever  been  raised  whether  these  rocks  are  conformable  or  un- 


^ 


*Tlie  tirtit  suggestions  of  volcanieiidmixtiireH  in  tlus  upper  Arciiean  rooks  of  central  Canada  were 
thrown  out  by  U.  M.  Dawson  in  tiis  desoriptiDn  of  the  agglomerates  of  tlie  Lake  of  the  Woods  ia 
the  Report  on  the  Cieology  and  Resources  of  the  49tli  Puralloi,  187'>,  p.  62. 


l.s-j 


A.  C.   I,ANVS(»N — m;i,ATInN,s  n\    Till;   AIM  IIKAN  U|'  (  ANADA. 


confornmble  u|><)ii  tlio  Liuirontiiiii ;  the  nsHUinption  hein^  al ways  that  both 
UHHcinblageH  of  roeka  wore  coinixised  of  inetutnor|)h()He(l  He<liinent».  The 
tuiHwer  WU8  held  to  hin^e  upon  the  punilleliHiii  or  abseneu  of  purulh^lirtin 
between  the  foliation  of  tht;  liuuntntian  granites  and  syenites  and  the  planes 
of  bedding  and  Hchi»to8ity  of  the  rocks  whit^h  are  in  eontaet  with  them.  Bell, 
Dawson,  Sclwyn,  and  McKellar  eontended  for  a  eonforniabie  setpienee. 
liO^an  is  silent  on  this  (piestion,  but  seems  to  have  been  in  no  doubt  as  to  the 
unconformable  superposition  of  the  true  Huronian  of  Lake  Huron  upon  the 
Laurcntian.  Hunt  has  always  (H)ntended  for  an  unconformity,  but  as  he 
also  had  in  mind  the  true  Huronian,  which  lie  once  regarded  as  Cambrian, 
his  contentions  do  not  seem  to  apply  to  such  rocks  as  are  clearly  Arcbean 
and  intimately  involved  with  the  Laurentian  gneisses.  It  is  therefore  fair 
to  say  that  the  drift  of  opinion  in  Canada,  and  probably  also  in  the  United 
States,  is  in  the  direction  of  conformable  8e(iuence  throughout  the  Archean, 
without  a  break  between  the  lower  (Laurcntian)  and  upper  (Ontarian) 
systems.  This  view  has  recently  been  emphatically  endorsed  by  Professor 
Alex.  Winchell*  as  a  result  of  his  observations  in  northern  Minnesota. 
Dawson  has  recently,  as  a  result  of  his  studies  of  analogous  conditions  on 
the  Pacific  coast,  thrown  over  his  earlier  opinions  as  to  the  conformable 
se(|uence  between  these  two  divisions  of  the  Archean  on  the  Lake  of  the 
AVoods,  and  is  now  in  accord  with  the  writer  as  to  the  nature  of  the  relations 
which  obtain  there,  and  which  will  be  set  forth  in  the  sequel.f 

Irruptive  Contact  on  Lake  of  the  Woods. —  Up  to  the  date  of  the  publication 
of  the  writer's  report  on  the  geology  of  the  Lake  of  the  Woods  (18M5), 
the  possibility  of  any  other  relationship  between  the  two  great  divisions  of 
the  Archean  than  those  of  conformity  or  unconformity  do  not  seem  to  have 
been  entertained.  In  that  report  the  writer  pointed  out  that  the  relation- 
ship was  one  of  neither  conformity  nor  unconformity,  but  of  an  entirely  dif- 
ferent order.  Evidence  was  adduced  in  some  detail  to  show  that  the  condi- 
tions of  the  contact  between  the  Laurentian  and  the  Keewatin  are  essentially 
those  which  obtain  between  any  Paleozoic  or  later  intrusion  of  granite  and 
the  bedded  rocks  through  which  it  breaks.  The  contact  was  shown  to  be 
a  brecciated  one,  the  gninltoid  <i,a  ;iss  ratnifying  through  the  schists  in 
a|)ophyses,  both  transverse  and  parallel  to  the  strike  of  the  schist,  and  hold- 
ing in  abundance  fragments  from  the  Keewatin  formations,  which  had  clearly 
been  broken  off  from  the  latter  while  it  was  in  a  hard  and  brittle  state  and 
had  found  their  way  into  the  Laurentian  often  for  considerable  distances 
from  the  contact,  as  well  as  more  notably  in  its  proximity.  The  conditions 
observed  indicate  clearly  that  we  had  no  (juestion  of  conformity  or  uncon- 
formity to  deal  with,  but  with  the  contact  of  an  irruptive  igneous  mass,  of 

*Geol.  and  Nat.  Hist.  Survey  of  Minnesota,  loth  Annual  Report,1886,  pp.  181,  100,  et  seq.;  Kith  An- 
nual Keport,  1887,  pp.  335,  330,'  300,  304,  et  seq. 
t  Annual  Keport  Geol.  Survey  of  Canada,  Vol.  II,  N.  S.,  1880,  p.  13u. 


\ 


lul 
inn 

of 


A 


s^ltl)lVls(u^^  <ti    Tin;  oniauian  >y.sti;m. 


ls:5 


^ 


later  foriiiHtioii  than  the  schintM  of  the  Keuwutin  Hcriui^,  and  breaking  through 
them. 

Irniptlvn  Con  tact  In  Jiuiny  Luke  Region. — The  studies  here  inaugurate*! 
ahout  Lake  of  the  Woods  have  since  been  continue<l  into  the  Kainy  hike 
region,  and  still  farther  eastward  to  Lake  Superior.  A  portion  of  the  re- 
sults are  contaiiMMl  in  a  recently  published  report  of  the  (iC(dogieal  Hurvey 
of  Canada.* 

Throughout  this  region,  it  was  found  that  the  Keewatin  is  not  the  only 
group  in  the  upper  division  of  the  Arehean,  but  that  another  very  volumi- 
nous group  intervenes  between  it  and  the  Laurentian,  to  which  the  name 
Coutchiching  has  been  given. f  The  relations  of  the  Laurentian  to  this 
group  of  schists  was  found  to  be  the  same  as  to  the  Keewatin,  with  even 
clearer  and  more  abundant  evidence  of  the  irruptive  and  later  origin  of  the 
Jiaurentian.  With  extended  observations  it  was  also  noted  that  the  bedded 
rocks  of  the  Ontarian  system,  whether  belonging  to  the  Keewatin  or  C.^out- 
chiching,  present  a  more  highly  altered  or  more  crystalline  and  schistose 
facies  in  proximity  to  the  contact  with  the  Laurentian  granite-gneiss  than  in 
the  middle  portions  of  the  trough,  where  the  rocks  are  frequently  not  greatly 
altered  from  the  normal  character  of  their  analogues  in  Paleozoic  formations. 

In  other  words,  there  is  evidence  of  contact  metamorphism  where  thj 
Laurentian  rocks  come  against  the  shattered  and  ragged  edge  of  the  local 
base  of  the  Ontarian  system.  All  the  conditions  of  contact,  therefore, 
whereby  we  recognize  any  mass  of  granite  to  be  irruptive  through  stratified 
rocks,  are  found  to  hold  here  between  the  rocks  cf  the  Laurentian  and  On- 
tarian systems.  The  detailed  geological  mapping  of  the  country  shows  also 
that  the  Laurentian  rocks,  while  continuoi^  beneath  the  schist  belts,  come 
to  the  surface  in  areas  which  may  be  described  as  isolated  bosses.  Each  of 
these  is  surrounded  by  a  belt  of  the  Ontarian  rocks,  usually  in  the  form  of  a 
sharply  folded  trough  sunk  down  into  the  Laurentian  and  separating  the 
surface  exposure  of  the  boss  from  those  of  its  neighbors.  These  belts  of  for- 
mations of  the  Ontarian  system  are,  for  tiie  most  part,  compact  and  con- 

*  Annual  Report,  1887,  Part  F. 

t  It  is  iinfortunatn  that  two  new  namos  have  become  current  for  this  grcup  of  rock-s.  The  term 
CoutcliiuiiinK  was  proposed  by  ttie  writer  in  a  paper  which  left  tiis  hands  in  Alarcli,  1887,  bearinK 
that  date,  and  which  was  published  in  the  Aniei'iean  Journal  of  Science  in  June  of  the  same  year. 
The  geological  position,  lithological  character,  known  geoi;raphical  distribution,  relations  to  Kee- 
watin and  Ijaurentia!!,  and  liie  importance  and  distinct  individuality  of  this  great  group,  were 
stated  and  discussed  in  that  paper,  in  the  Kifteentli  Annual  Report  of  the  Geological  Survey  of 
Minnesota,  bearing  the  date  of  May  1, 1887,  but  appearing  much  later,  tiiere  is  a  multitude  of  valu- 
uble  observations  and  details,  but  no  systematic  statement  of  the  geology  of  the  region ;  and  the 
ditt'erentiation  of  the  group  in  question,  as  geologically  separable  from  the  rest  of  the  complex, 
does  not  appear  to  have  been  recognized  at  the  time  of  the  writing  of  the  report,  altliough  the  term 
"  Vermilion  series'"  occurs  once,  apparently  as  an  afterthought,  inserted  on  page  2>.t!)  of  Professor 
N.  H.  Winchell's  report.  On  the  maps  accompanying  the  report,  however,  it  is  distinguished 
clearly  by  a  color  and  named  the  "  Vermilion  series,"  although  here  including  formations  that  had 
earlier  been  designated  Keewatin.  From  this  it  would  appear  that  the  term  "  Coutchiching"  was 
somewhat  prior  to  "  Vermilion,"  and  was  more  fully  and  precisely  defined  as  to  its  geological  sig- 
nificance. Moreover,  the  term  "Vermilion  Ijake  series"  was  used  earlier  by  Irving  in  another 
sense  than  that  proposed  by  Professor  N.  II.  Winchell,  and  in  the  same  Annual  Report  (Fifteenth) 
the  terms  "Vermilion  series"  and  "Vermilion  system"  are  used  by  Professor  A.  Winchell,  on  pp. 
192, 1U5, 100,  in  another  and  much  more  comprehensive,  but  still  undefined,  sense. 


)    i 


184 


A.  C.  I.AWSON — KKLATJONS  Ol"  TIIK  AUCllKAX  UF  CANADA. 


tinuous,  forming  a  great  anastomosing  mesh-work,  the  general  strike  being 
always  concave  to  the  Laurentian  areas  which  they  encircle. 

Sometimes,  however,  where  denudation  has  exposed  their  deeper  portions 
along  anticlinal  or  synclinal  ares,  as  in  parts  of  the  Lake  of  the  AVoods  and 
Kainy  lake  regions,  and  better  in  Hunter's  island,  the  formations  in  contact 
with  the  Laurentian  granite-gneiss  are  finind  to  be  excessively  shattered,  and 
countless  numbers  of  fragments  are  strewn  throughout  the  nuiss  of  the  ir- 
ruptive  rocks.  The  country  is  well  bared,  and  what  is  stated  is  clearly  visi- 
ble on  well-exposed  continuous  rock  surfaces.  These  included  detached 
fragments  of  the  formations  overlying  the  granite-gneiss  range  in  size  from 
pieces  a  few  inches  across  to  immense  masses.  Their  longest  diameters  are, 
as  would  be  expected,  in  the  plane  of  schistosity.  Where  the  enclosing  rock 
is  gneissic,  the  inclusions  have  usually  a  constant  orientation  parallel  to  the 
foliation  of  the  gneiss,  which  also  coincides,  as  a  rule,  with  the  nearest  edge 
of  the  belt  through  which  it  breaks,  where  not  too  remote  from  the  edge. 
Other  inclusions  in  the  Laurentian  have  been  observed  whose  derivation 
from  the  Ontarian  rocks  cannot  be  established.  Suggestions  as  to  their 
origin  have  been  thrown  out  by  the  writer  in  his  report  on  the  Rainy  lake 


region. 


Along  the  edges  of  the  belts  of  the  Ontarian  rocks,  there  may  frequently 
be  observed,  running  out  from  the  niain  belt  and  in  continuous  strike  with 
it,  tongues  of  schist  which  taper  more  or  less  gradually  and  eventually  end 
in  ])oints.  These  also  are  seen  to  be  immersed  and  congealed  in  the  granite- 
gneiss  ;  and  numy  of  the  larger  detached  inclusions  are  doubtless  portions 
of  such  tongues  which  have  been  septuated  from  the  main  belt  by  the  low- 
ering of  the  plane  of  surface  truncation  by  denudation,  rather  than  by  actual 
detachment  at  the  time  of  disturbance.  This  would  in  a  large  measure 
account  for  the  fact  that  the  common  orientation  of  the  lax'ger  fragments, 
and  their  parallelism  with  the  edge  of  the  belt,  holds  for  the  dip  as  well  as 
the  strike. 

Numerous  long,  attenuated,  [)arali«!l  tongues  arc  also  formed  at  the  edges 
of  the  schist  belts  by  the  injection  along  the  planes  of  schistosity  of  portions 
of  the  granite-gneiss  magma,  forming  an  evei.ly  ribboned  alternation  which 
simulates  bedding.  Its  formation  by  injection  is,  however,  sufficiently 
ai)[)arent.  Similar  ribboned  alternations  are  described  and  figured  by  Bar- 
rois*  as  occurring  at  the  edge  of  the  Cambrian  schists  of  Brittany,  where 
pierced  by  irruptive  granites.  The  detached  inclusions  are,  also,  not  in- 
fre(iuently  ribboned,  parallel  to  the  schist  planes,  with  apophyses  from  the 
main  area  of  the  enclosing  granite-gneiss. 

If,  at  the  base  of  the  Ontarian  system,  wv  had  bedded  rocks  which  on 
metamorphisni  gave  rise  to  crystalline  limestones,  (juart/ites,  etc.,  we  would 


*  Hull.  Soe.  (.ieol.  de  France,  ;ttne  Serie,  t.  Xl\',  188ii,  p.  833. 


rossinMo  oRiriiN  or  pskido  p.kddino. 


isr, 


edges 


have  these  involved  with  the  Laureiitian  gneiss,  just  as  the  hornblende 
schists  and  mica  schists  are,  and  intercalations  would  be  produced  which 
would,  as  in  the  case  of  the  schists,  frequently  simulate  interbedding  of 
quartzite  or  limestone,  as  the  case  might  be,  with  the  gneiss.  The  deception 
would,  of  course,  be  intensified  by  subsequent  further  defornuition  of  the 
crust  by  pressure  so  as  to  be  practically  beyond  detection,  if  the  clue  were 
not  followed  up  from  a  starting  point  where  such  subsequent  dynamic 
agencies  have  not  obscured  the  true  relationship.  This,  the  writer  is  per- 
suaded, is  the  explanation  of  many  of  the  intimate  associations  of  gneiss  and 
(|uartzite  or  limestone,  whereby  rocks  really  metamorphic  sediments  are  so 
involved  and  welded  with  rocks  of  plutonic  irruptive  origin  that  they  have 
been  taken  together  as  a  simple  secpience  of  deposited  strata. 

In  some  portions  of  the  Laurentian  country,  which  the  attitude  of  the 
flanking  rocks  indicates  was  once  arched  over  by  an  anticlinal  dome  of  the 
latter,  there  .are  found  patches  of  schist  lying  quite  flat,  or  nearly  so,  upon 
the  granite,  showing,  in  favorable  clirt"  sections,  a  brecciated  or  intrusive 
contact  on  the  under  side.  These  reinnants  seem  to  show  that  the  anticlinal 
dome  was  flat  or  very  lowly  rounded,  and  that  only  on  the  flanks  of  the 
Laurentian  boss  did  the  strata  composing  the  arch  i)lunge  down  at  high 
angles. 

Significance  of  Relatlomhlp. — Bearing  in  mind  the  essential  distinctions 
which  exist  between  the  rock  formations  of  the  Ontarlan  and  Laurentian 
systems,  both  as  to  their  lithological  character  and  their  mode  of  occurrence^ 
and  remembering  also  their  relative  geographical  distribution,  the  foregoing 
statement  of  the  relationship  which  obtains  between  the  two  systems  leads 
clearly  and  unavoidably  to  this  conclusion,  viz.,  that  the  formations  of  the 
Ontarian  system  at  one  time  rested,  as  a  volume  of  hard  rocks,  upon  a 
magma  which  subsequently  crystallized  as  the  Laurentian  granite-gneiss ; 
so  that  the  present  line  of  demarkation  between  the  two  systtaus  must  be 
regarded  as  representing  the  trace  of  what  was  once  a  plane  of  contact 
between  the  then  crust  and  tiie  magma  upon  which  it  floated. 

This  conclusion  aflf'ords  us  a  conception  of  the  Archean  which  is  ideal  in 
its  simplicity  and  which  gives  us  the  key  to  the  raveling  of  the  mystery  in 
which  the  subject  has  been  involved.  Tlie  fact  that  the  crust,  which  con- 
stitutes what  we  now  call  the  Ontarian  system,  was  crumjjled  while  it  floated 
on  the  magma ;  the  fact  that  its  lower  portions  were  shattered  by  disturbance 
so  that  the  magma  penetrated  the  fissures  and  enclosed  detached  fragments  ; 
the  fact  that  there  were  currents  in  the  magma  which  arranged  the  inclusions 
in  streams  and  also  i)roduced  the  foliation  of  the  gneiss  ;  the  fact  of  contact 
metamorphism — all  these  are  incidental  and  concomitant  circumstances  of 
the  great  essential  condition  ol'a  crust  resting  on  a  magma. 

JJut  from  the  nature  of  the  rocks  of  the  Ontarian  system  it  is  clear  that 


.i 


ISO 


A.  ('.  T,A\VSON — 1;KF-ATI0\S  or  TMK  Al.TIIKAX  OF  CAXADA. 


1    f 


they  could  not  have  been  deposited  upon  a  magnui.  There  must  have  been 
a  firm  crust  presenting  a  floor  uj)on  which  they  were  laid  down.  That  floor, 
together  with  portions  of  the  system  of  rocks  which  lay  piled  upon  it,  has 
disappeared.  That  it  has  sunk  down  to  a  zone  of  fusion  and  become  ab- 
sorbed by  liquefaction  in  a  sub-crustal  magma,  which  later  crystallized  out 
as  the  Laurentian,  is  the  only  explanation  that  is  open  to  us.  It  follows 
also  that  the  Laurentian  rocks  are  younger  than  those  of  the  Ontarian  sys- 
tem, as  has  been  before  indicated. 


PRiNrrpLEs  OF  Classfficatton. 


I'!- 


The  bearing  of  the  facts  and  conclusions  recorded  above  upon  the  tax- 
onomy of  the  Archean  is  apparent.  The  argument  establishes  this  cardinal 
princii)le  in  the  classification  of  that  great  complex  of  rocks,  viz.,  that  its 
primary  subdivision  depends  upon  a  distinction  of  cosmical  importance  be- 
tween an  older  assemblage  of  altered  normal  surface- formed  strata  and  a 
younger  assemblage  of  rocks  resulting  from  the  crystallization  of  a  sub- 
crustal  magma. 

Principles  applicable  to  the  Upper  Division. — To  the  upper  or  Ontarian 
system  the  ordinary  stratigraphical  methods  of  classification  are  applicable. 
The  system  separates  stratigraphically  into  two  great  groups.  The  lower 
and  older,  consisting  of  strata  free  from  volcanic  admixtures,  so  far  as  has 
been  observed,  is  the  Coutchiching.  It  resembles  in  its  lithological  charac- 
ters and  in  its  position  the  Montalban  of  Hitchcock.  The  upper  group, 
consisting  of  rocks  which  are  dominantly  volcanic  in  composition,  is  the 
Keewatin.  It  rests  upon  the  Coutchiching  in  probable  unconformity,  the 
l)eginning  of  the  period  in  which  these  rocks  were  deposited  being  signalized 
by  the  advent  of  a  widespread  and  continued  volcanic  activity.  This  group 
falls  into  line  with  the  Green  Mountain  series  in  the  position  assigned  to  it 
by  Hitchcock.  Other  groups  may  quite  possibly  be  discovered  which  will 
swell  the  volume  of  the  Ontarian  system. 

Principles  applicable  to  the  Lower  Division. — In  the  Laurentian  the  ordi- 
nary stratigraphical  principles  of  classification  do  not  apply,  since  there  are 
no  strata  properly  so  called  ;  and  we  must  seek  for  a  principle  appropriate 
to  an  assenil)lage  of  rocks  essentially  different  in  their  development  and 
mode  of  occurrence  from  all  those  of  the  stratigraphical  column.  The  Lau- 
rentian is  not  homogeneous  throughout  its  surface  distribution.  It  is  com- 
l)osed  of  different  members  or  masses,  which,  while  they  present  wonderfully 
constant  general  characters  within  themselves,  are  distinct  from  one  another 
lithologically.  A  study  of  the  relationship  between  the  masses  thus  differen- 
tiated in  space  leads  us  to  the  chief  moment  of  all  geological  classification, 
namely,  their  differentiation  in  time  ;  and  we  have  to  consider  the  possibility 


SUI'.DI VISIONS   OF    TIIH    LAURENTIAN   SYSTF-M. 


187 


)^ 


of  different  generations  of  Laurentian  rocks.  This  possibility  presents  itself 
as  soon  as  we  familiarize  ourselves  with  the  sub-crustal  igneous  and  later 
formations  of  the  Laurentian. 

Different  Generations  of  Laurentian  Bocks. — To  the  writer  this  conception 
of  different  generations  has  never  been  more  than  a  possibility  till  the  present 
year.  In  his  report  on  the  Rainy  lake  region,  two  broadly  distinct  mem- 
bers of  the  Laurentian  were  distinguished,  lithologically  and  on  account  of 
their  systematic  relative  distribution,  as  the  "  peripheral  zone"  and  "  inner 
nucleus  "  of  the  Stanjikoming  area,  the  former  being  composed  chiefly  of 
hornblende-granite  and  syenite-gneiss,  and  the  latter  of  very  quartzose 
biotite-gneiss.  The  relationship  in  time  between  these  two  rock  masses  re- 
mained indeterminate.  During  the  past  summer,  however,  he  has  been  able 
to  establish,  in  the  Hunter's  island  region,  chronologically  distinct  genera- 
tions of  Laurentian  gneisses.  In  that  region  there  are  two  broadly  distinct 
members  of  the  Laurentian,  analogous  petrographically  and  in  relative  dis- 
tribution to  those  of  the  Stanjikoming  area.  Belov  the  Keewatin  rocks 
there  is  a  great  mass  of  hornblende-granite-gneiss,  which  presents  an  irrup- 
tive  or  intrusive  contact  against  them.  Towards  the  central  part  of  Hun- 
ter's island  this  hornblende-granite-gneiss  is  pierced  by  an  enormous  irrup- 
tion of  biotite-grauite,  which  is  sometimes  very  distinctly  gneissic  and 
sometimes  quite  undifferentiated  in  structure.  In  texture  it  varies  from 
fine-grained,  almost  micro-granitic,  to  a  moderately  coarse  granite.  This 
biotite-grauite-gneiss  traverses  the  horublende-grauite-gneiss  in  innumerable 
clearly  defined  dikes  cutting  it  in  all  directions,  and  holds  innumerable  in- 
cluded blocks  of  the  same  rock.  It  comes  up  from  beneath  the  hornblende- 
granite-gneiss,  and  is  unquestionably  of  later  age. 

Thus  we  have  in  this  area  at  least  two  distinct  generations  of  Laurentian 
rocks,  both  the  result  of  the  crystallization  of  a  sub-crustal  magma.  At  the 
time  of  the  second  generation  the  rocks  of  the  first  generation  constituted 
the  lower  portion  of  the  crust. 

It  is  upon  the  recognition  of  facts  of  this  order  that  an  intelligible  and 
profitable  classification  of  the  Laurentian  rock  masces  and  the  geological 
events  which  they  represent  must  be  established. 

Other  Conditions  considered. — The  relationship  which  has  been  found  to 
obtain  between  the  upper  and  lower  Archean  leads,  as  has  been  said,  to  a 
conception  which  is  at  once  grand  and  simple.  So  long  as  we  confine  our- 
selves to  regions  like  that  northwest  of  Lake  Superior,  where  no  great  com- 
plications have  been  introduced  by  post-Archean  crust-crumpling  agencies, 
it  affords  a  full  explanation  of  all  the  phenomena  of  Archean  geology. 

There  is  a  possible  simpler  case  which  would  still  present  the  essential 
conditions  of  the  relationship  in  question ;  i.  e.,  the  case  in  which  the  sub- 

XXV— Bum,.  Gf.oi..  Soc.  Am.,  Vol.  1,  1889. 


188 


A.  C.  LAWSON — KRr-ATIO\S  OF  TIIK  AUrFIKAN  OP  f'ANADA. 


crustal  magma  might  be  irrupted  within  the  overlying  crustal  rocks  without 
the  intense  folding  of  the  latter.  Here  we  should  expect  to  find  a  less  pro- 
nounced alteration,  due  only  to  the  proximity  of  the  magma,  and  an  absence 
of  those  phases  of  metamorphism  which  accompany  the  rock  shearing,  crush- 
ing, and  stretching  due  to  dynamic  ageinries.  In  the  common  case,  where 
the  upper  crustal  rocks  are  folded,  varying  phenomena  would  also  be  ob- 
served according  as  the  folding  took  place  before  the  fusion  which  produced 
the  magma  immediately  beneath  the  crust  or  while  the  latter  was  floating 
upon  the  magma. 

There  are  also  more  complicated  cases  which  are  doubtless  common. 
These  are  due  to  the  superimposed  action  of  crust-crumpling,  rock-shearing, 
strata-squeezing  forces  subsequent  to  the  establishment  of  the  Archean  con- 
ditions in  their  primal  simplicity.  These  are  possibilities  which  must  be 
borne  in  mind  in  attempts  to  apply  the  theory  here  advanced  to  the  Archean 
in  other  regions.  It  is  easily  conceivable  that  had  the  country  northwest  of 
Lake  Superior  been  subjected  to  extensive  deformation  in  post- Archean 
times,  the  evidence  whereby  the  irruptive  character  of  the  Laureutian  has 
been  demonstrated  might  have  been  entirely  obscured,  and  the  true  relation- 
ship might  have  remained  unsuspected,  as  appears  to  have  been  the  case  in 
better  known  regions. 


C. 


Similar  Observations  elsewhere. 


In  various  parts  of  the  world  observations  have  been  recorded  which  show 
that  the  phenomena  arising  from  the  irruption  of  a  local  or  general  sub- 
crustal  magma  through  an  overlying  crust,  and  the  consequent  development 
of  a  complex  of  gneissic  igneous  rocks  and  nietamorphic  strata,  are  not 
peculiar  to  the  region  studied  by  the  writer. 

MacFarlane  *  long  ago  described  and  figured  good  evidence  of  the  irrup- 
tive character  of  the  Laurentian  of  the  northeast  shore  of  Lake  Superior ; 
but,  in  accordance  with  the  views  of  the  extreme  plutonic  school,  he  regarded 
the  whole  complex  of  intrusive  and  intruded  rocks  as  the  first  crust  of  the 
earth,  and  the  angular  fragments  of  hornblende  schist  as  earlier  separations 
from  the  same  magma  as  that  which  crystallized  into  the  Laurentian  granite 
or  syenite-gneiss. 

Mr.  Frank  Adams,  who  has  been  for  some  years  past  engaged  in  a  study 
of  the  Laureutian  of  the  Province  of  Quebec,  north  of  the  St.  Lawrence, 
says — 

"  Tlio  unexpected  tiict  was  ascertained  that  the  so-called  massive  and  stratified 
varieties  of  this  rocic  [aiiorthosite ;  hitherto  regarded  as  upper  Laurentian  and  meta- 


*  Geological  Formations  of  Lake  Superioi.    Canadian  Naturalist,  N.  S.,  Vol.  Ill,  1867,  p.  177. 


OBSERVATIONS   IN    EASTERN   CANaDA   AND   EUROPE. 


189 


7. 


morphicj  are  in  reality  only  different  portions  of  one  and  the  same  mass.  *  *  *  As 
a  re'sult  of  this  summer's  work,  I  thini<  it  may  bo  safely  concluded  that  the  rocks  com- 
prising the  principal  area  of  anorthosito  above  referred  to,  us  well  as  most,  if  not  all, 
of  the  smaller  areas,  are  of  eruptive  origin."  * 

He  confirms  this  in  his  summary  for  1888  in  the  following  words : — 

"  All  the  areas  of  anorthosite  now  known  to  occur  in  the  district  have  been  ex- 
amined, and  mapped,  and  have  proved  to  bo  either  eruptive  masses  cutting  through 
the  gneisses,  or  masses  interstratilied  with  the  latter,  but  probably  still  of  eruptive 
origin."  f 

Callaway  has  shown,  in  his  paper  on  the  granitic  and  schistose  rocks  of 
northern  Donegal,  that  the  granite-gneisses  of  that  region,  which  have  been 
regarded  as  Laurentian  and  which  correspond  closely  in  lithological 
characters  and  mode  of  occurrence  with  the  Laurentian  of  Canada,  are  really 
irruptive  through  older  rocks,  which  must  have  arched  them  over,  and  present 
all  the  evidences  of  irruption  which  have  been  adduced  by  the  writer  in 
support  of  the  irruptive  origin  of  the  Laurentian  northwest  of  Lake  Superior. 
He  thus  states  his  conclusions : — 

"1.  The  granite  rock  of  northern  Donegal,  originally  supposed  to  be  the  result  of 
the  metamorphism  of  sedin  ents,  and  recently  referred  to  the  Laurentian  system,  is  a 
true  igneous  granite,  as  seen  in  its  intrusion  into  the  adjacent  schists,  in  its  inclusions 
of  masses  and  fragments  of  other  rocks,  and  in  its  metaniorphic  action  on  limestone 
in  contact.  2.  This  granite  is  distinctly  foliated,  the  gneissic  structure  being  caused 
by  lateral  pressure,  *  *  *  3.  The  granite  is  intrusive  in  a  thick  group  of  quartz- 
ites,  quartz-schists,  hornblendic,  micaceous  and  talcose  (?)  schists,  and  crystalline 
limestones,  called  the  Kilmacrenan  series.  These  rocks  are  truly  crystalline,  but 
usually  thin-bedded  and  fine-grained.  4.  The  crystalline  schists  are  bounded  on  the 
east  by  a  semi-crystalline  series,  consisting  of  quartzose  grits  and  itacolumites,  quartz- 
ites,  crystalline  limestones,  compact  dolomites,  phyllites,  interlaminations  of  grit  and 
schistose  matter,  and  finely  foliated  micaceous  schists."  J 

These  conclusions  as  to  the  irruptive  origin  of  the  gneiss  are  confirmed  by 
later  observations  of  the  same  investigator  on  the  Galwuy  gneiss.  § 

In  the  pre-Caiubrian  or  Arciiean  of  Brittany,  Barrois  recognizes  the  irrup- 
tive character  of  the  gneisses  which  correspond  to  our  Laurentian.  He 
says — 

*'  Ces  gneiss  alternent  avec  des  lits  interstratifles  de  micaschistes  et  d'amphibolites, 
et  passent  h  des  granites  gneissiques  qui  les  penotrent  ti  la  fa9on  d'une  roche  eruptive. 
L'ensemble  des  gneiss  et  micaschistes  (/rmutlqaes  avec  granites  gneissiques  rappelle  par 
ses  caracteres  lithologiquos  Vetagc  ditncticn,  propose  par  M.  Hicks,  dans  le  pays 
de  Galles,  le  gneiss  fondamental  d'Ecosse,  certains   gneiss  laurentiens  du  Canada, 

*Geol.  Survey  of  Canada,  Summary  Report  for  1887  and  1888,  188SJ,  p.  ZIk. 

t  Ibid.,  p.  85a. 

jliuart.  Jour.  Geol.  Soc,  Vol.  XLI,  1885,  p.  239. 

Itjuart.  Jour.  Geol.  Soc,  Vol.  XLIII,  1887,  p.  517. 


X 


190        A.  C.  LAW.SON — KKLATIONS  OF  Tilt;  AKCIIEAX  OF  CANADA. 

*  *  *.  lis  [micaschistos]  y  alternent  iivec  des  lits  subordonnos  do  gneiss  h  gmiiis 
fins,  d'amphibulitcs,  de  chlorito  sehistcs,  do  schistos  micuoos,  et  compronnent  des 
masses  interstruti floes  de  diorites  et  de  granulites,  d'origino  eruptive.  Ces  ruclios 
subordonnees  forment  uvec  les  inieiisohistes,  diips  lesquels  elles  sont  injectees,  de 
longues  bandes  parallelcs,     *     *    *."* 

Newtou's  description  of  the  geology  of  the  Bhick  Hills  of  Dakota  f  leaves 
little  room  for  doubt  but  that  the  rocks  which  he  calls  Archean  correspond 
to  the  upper  Archean  or  Ontarian  system  of  central  Canada,  and  that  his 
irruptive  granite,  though  not  described  as  foliated,  is  the  analogue  of  the 
commonest  phase  of  the  Laurentian.  The  same  relationship  holds  between 
the  two  rock  systems  in  both  regions,  and  many  of  the  Laurentian  granites 
are  devoid  of  foliation. 


J. 


Geognostical  Equivalents  of  the  Archean. 

In  iissemblages  of  rocks  of  indeterminate  or  post-Archean  age  complexes 
of  gneissic  irruptive  rocks  and  older  metamorphic  strata  of  clastic  or  vol- 
canic origin  are  now  well  known.  These  cannot  be  spoken  of  as  the  geolog- 
ical equivalents  of  the  Archean  complex  on  account  of  their  diverse  age,  but 
may  be  referred  to  as  its  geognostical  equivalents,  since  their  development 
appears  to  depend  upon  universal  sub-crustal  conditions,  which  are  to  a  large 
extent  independent  of  geological  age. 

McMahon,;}:  in  his  studies  of  the  great  "  central  gneiss  "  formation  of  the 
Himalaya  mountains,  has  demonstrated  clearly  that  the  formation  is  not,  as 
was  long  supposed,  the  Archean  basement  upon  which  the  Paleozoic  sedi- 
ments were  deposited,  but  is  an  irruptive  mass  breaking  up  through  the 
Silurian  and  later  rocks,  altering  them,  holding  detached  fragments  of  their 
strata,  and  being  injected  within  the  strata.  Speaking  of  this  formation, 
which  he  calls  gneissose  granite,  he  cites  the  following  evidences  in  proof  of 
its  irruptive  origin  :  1.  The  granite  has  produced  a  certain  amount  of  con- 
tact metamorphism  on  the  rocks  touching  it.  2.  Tongues  and  intrusive 
veins  have  been  sent  from  the  granite  into  the  adjoining  rocks ;  in  other 
places  the  granite  appears  in  sheets  between  the  beds  of  the  sedimentary 
rocks  at  some  distance  from  the  junction  of  the  latter  with  the  main  mass  of 
the  granite,  and  in  some  cases  these  sheets  or  dikes  have  cut  through  tlie 
beds  and  passed  from  one  horizon  to  another.  3.  The  main  mass  of  the 
granite  appears  at  different  geological  horizons. §     4.  The  granite  contains 


'•feii'iicture  Oieologique  du  FinisWre.   Bull.  Soc.  Geol.  de  France,  .3me  Serie,  t.  XIV,  1886,  p.  657. 

t  Report  on  the  Geology  md  Re.Mources  of  the  Black  Hills  of  Dakota.  By  Henry  JJewton  and 
Walter  P.  .Jenney,  Washington,  1880,  pp.  4.V8(),  220-2!i2. 

IGeol.  Survey  of  India,  ieconls,  Vol.  XVIIl,  Part  4, 1884,  p.  168;  ibid.,  Vol.  XVIII,  Fart  2,1885, 
p.  7!t.    Geol.  Mag.,  N.  S.,  Lccade  III,  Vol.  IV,  1887,  p.  212. 

^  Ah  it  does  when  it  cotncH  at  one  place  against  the  ICeew.itin  and  at  another  against  the  Cout- 
chiching  in  the  Rainy  lake  region. 


OKANITIC    IKKll'TlONS   UF    VAKIOLS   AUKS. 


191 


veins  similar  to  those  caused  by  shrinkage  on  cooling  in  granite  of  admit* 
tedly  eruptive  origin,  5.  It  contains  fragments  of  slates  and  schists  im- 
bedded in  it.  He  also  states  that  the  evidence  afforded  by  the  study  of  thin 
slices  confirms  the  conclusion  arrived  at  'jy  the  stratigraphical  evidence,  and 
gives  a  summary  of  the  microscopic  evidence.* 

The  very  able  and  precise  descriptions  by  Barroisf  of  the  various  granitic 
irruptions  which  have  affected  Brittany  at  different  ages  from  the  pre-Cam- 
brian  up  to  the  Carboniferous  show  beyond  (luestion  that  not  only  in 
Archean  times,  but  at  various  subsequent  j)eriod8  were  the  conditions 
which  characterize  the  Archean  of  Canada  reproduced.  He  describes  par- 
ticularly the  "  granite  gneissique,"  demonstrates  its  irruptive  origin,  and 
notes  not  only  the  contact  metamorphism,  but  also  the  injection  of  these 
rocks  "en  filonnets  minces  et  repetes"  within  the  encasing  schists.  His 
descriptions  and  figures  of  repeated  injections  of  granite  within  the  schists, 
so  as  to  produce  an  alternation  simulating  bedding,  closely  corresponds  with 
the  contact  phenomena  described  by  tlie  writer  as  observed  between  the 
Laurentian  and  Keewatin  on  the  Lake  of  the  Woods,  the  interpretation  of 
which  is  entirely  in  accord  with  that  of  Barrois,  though  questioned  by  Pro- 
fessor A.  Winchell.J  It  would  appear  that  just  as  in  Hunter's  island,  north- 
west of  Lake  Superior,  we  have  two  generations  of  Laurentian  rocks  from  a 
sub-crustal  magma,  so  in  Brittany  there  have  been  several  generations  of 
similar  rocks  breaking  through  the  overlying  crust,  extending  in  time  as 
late  as  the  Carboniferous. 

In  Norway  Kjerulf  4^  places  the  "  Gebanderte  granit,  oder  gneisgranit " 
with  the  eruptive  rocks,  and  states  that  in  numberless  places  such  rocks 
break  through  the  strata  of  the  gruudgebirges,  and  also,  indeed,  through  the 
Bergenschiefer  in  which  Reusch  has  since  found  Silurian  fossils.] |  In  the 
greater  part  of  Norway  he  says  (translated  freely)  ^j  — 

"  What  was  formerly  recognized  as  gneiss  must  on  the  map  be  now  designated  as 
granite.  Tlie  reasim  why  the  older  observers  o.scumo  it  to  be  gneiss  is  the  granular 
banded  structure,  which  we  must  distinguish  from  the  appearance  of  bedding.  On 
older  maps  are  shown  also  other  great  regions  in  which  the  dip  and  s>ike  of  the  beds 
is  given,  an  attribute  which  they  do  not  in  reality  possess;  and  t'le  reason  for  this 
lies  in  the  confounding  of  foliation  with  beddine;.  *  *  *  The  rock,  according  to 
the  old  conception,  is  granite  when  no  bedding  occurs  in  it.  The  modern  view, 
which  had  already'  been  announced  by  Delesse,  says  :  '  En  realite  c'est  [le  gneiss  granit] 
seulement  uno  variete  du  granit,  qui  est  voinee  et  qui  parait  avoir  ete  genee  dans  sa 
cristallisation.' 


■>** 


*Geol.  Mag.,  loc.  cit. 

t  Hull.  Soc.  Geol.  de  France,  3me  Serie,  t.  XIV,  1880,  pp.  fi5,')-8'J8. 

j(ieol.  Sin-vey  oj  Minnesota,  Fifteenth  Annual  Keport.  1886,  p.  201,  js  5. 

gl>ie  Geologic  des  Slid,  und  Mit.  Norwfgen,  Honn,  1880,  p.  '£iT. 

li  Fossil ieii  Fulirenden  Scliiefer  von  liergen,  Leipi^ig,  188a. 

11  Op.  cit.  p.  282. 

**  Delesse,  Etudes  sur  le  Metamorphism,  1801. 


V.)2 


A.  0.  LAWSON — KELATIONS  OF  THE  AKCHEAN  OF  CANADA. 


The  syenites  of  the  southeast  coast  of  Norway,  also,  which  have  been  studied 
particularly  by  Bnigger,  and  which  are  irruptive  through  fossiliferous 
Silurian  and  Devonian  strata,  are  eminently  gneissic  in  places.  They  are  in- 
distinguishable in  this  respect  from  the  more  distinctly  foliated  varieties  of 
our  Laurentian  gneiss. 

Lehman's  masterly  work-'-  on  the  rocks  of  Saxony  and  other  geologically 
similar  regions  has  clearly  established  that  many  of  the  gneisses  of  central 
Europe  are  irruptive  in  their  origin. 

The  foliated  gabbros  or  gabbro-gneisses  of  the  Lizard  are  regarded  as 
eruptive  by  such  eminent  observers  as  Teall  f  and  McMahon,|  though  they 
differ  as  to  the  precise  mode  of  the  development  of  the  foliation. 

Harper  §  has  shown  that  the  "granite  and  gneissic  granite"  of  Larn, 
Caernarvonshire,  which  was  formerly  held  to  be  Archean,  is  in  reality  irrup- 
tive and  of  more  recent  age  than  the  Upper  Arenig  strata  : 

"  The  actual  contact  of  the  two  rocks  is  easily  found,  and  the  granite  is  seen  to  send 
out  little  tongues  between  the  laminio  of  the  shale.  Specimens  of  the  latter  rock, 
indurated  and  lirnily  adhering  to  the  granite,  may  be  obtained.  *  *  ^  The  shale 
is  clearly  altered  and  exhibits  little  spots  and  nodules  supposed  to  nfpresent  the  in- 
cipient development  of  chiastolite.  Another  quarry,  well  within  the  boundary  of 
the  granite,  shows  entangled  masses  of  baked  shales." 

In  a  paper  submitted  to  the  International  Geological  Congress  at  its  Lon- 
don session  ||  in  1888,  the  writer  quoted  Dr.  G.  M.  Dawson  ^[  at  some  length 
to  show  how  entirely  the  conditions  which  obtain  between  the  Triassic  rocks 
of  the  west  coast  and  the  younger  subjacent  irruptive  granite  are  analogous 
to  those  which  obtain  between  the  rocks  of  the  upper  Archean  or  Ontarian 
system  and  the  Laurentian  granite  gneiss.  Dr.  Dawson's  account  of  the 
history  of  geological  events  in  that  region  in  post-Triassic  times  confirms 
the  correctness  of  the  writer's  interpretation  of  the  Archean  of  central 
Canada. 

The  interesting  geognostical  equivalent  of  the  Archean  on  the  Pacific 
coast  is  paralleled  on  the  Atlantic  coast  by  the  great  irruption  of  "gneissic 
granites"  which  in  post-Cambrian  times,  possibly  as  late  as  the  Devonian, 
have  broken  up  through  the  Cambrian  slates  and  quartzites.**  These 
"  gneissic  granites "  are  indistinguisable  from  many  of  the  Laurentian 
gneisses. 


♦Untersuchungen  iiberdie  Entstehunt;  der  altkrystallinischen  Schiefergeateine,  Bonn,  1881. 
t  Origin  of  Certain  Handed  Gneisses;  Geol.  Mag.,  N.  S.,  Decade  III,  Vol.  TV,  1887,  p.  484. 
fOn  the  Foliation  of  the  Lizard  (Tabbro;  ibid.,  p.  74. 
jiCiuart.  Jour.  Geol.  Soc,  Vol.  XXX IV,  1878,  p.  442. 
II  Ktude.s  siir  les  schistes  eristallins,  p.  (id. 

if  Geol.  Survey  of  Canada,  Annual  lleport,  1887,  Part  H,  pp.  II-IH. 

**The  Lower  Cambrian  rocks  of  (iuysborougli  and  Halifax  Counties,  N.  S.    By  E.  R.  Faribault; 
(ieol.  Survey  of  Canada,  Annual  Report,  1880,  Part  P,  p.  l-M. 


t.V 


f 


lie 

lis 


« 


The  Akoumknt  fisom  Analogy. 

These  references  and  (jiiotations  by  no  means  exhaust  the  literature  of 
the  subject.  They  are  taken  mostly  from  very  recent  writings,  and  much 
to  the  same  effect  might  be  quoted  from  the  older  geologists,  such  as  Von 
Cotta,  Neumann,  Darwin,  Delesse,  and  others,  who  have  insisted  on  the  ir- 
ruptive  character  of  gneissic  rocks  or  have  regarded  gneiss  as  but  a  differ- 
entiated variety  of  irruptive  granite.  But  enough  has  been  adduced  to 
show  that  the  writer's  interpretation  of  the  Archean  geology  of  central 
Canada,  in  so  far  as  it  depends  upon  the  irruptive  nature  of  the  Lauren tian 
gneisses,  is  not  without  the  strong  support  of  many  analogies. 


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